Yabing Qi, Okinawa Institute of Science and Technology
Wei Huang, Nanjing Tech University
Nam-Gyu Park, Sungkyunkwan University
Kai Zhu, National Renewable Energy Laboratory
Applied Physics Letters | AIP Publishing
The Journal of Physical Chemistry Letters | ACS Publications
National Renewable Energy Laboratory
Nature Energy | Springer Nature
Science Magazine| AAAS
Wiley VCH Verlag GmbH &
ES1.1: Commercialization, Synthesis, Large Area and Modules
Monday PM, April 17, 2017
PCC North, 200 Level, Room 224 B
9:00 AM - ES1.1.01
Solid-State Ligand-Exchange Fabrication of CH3NH3PbI3 Capped PbS Quantum Dot Solar Cells
Jiajun Peng 1 , Yani Chen 1 , Ziqi Liang 1 Show Abstract
1 , Fudan University, Shanghai China
Lead sulfide (PbS) colloidal quantum dots (CQDs) have emerged as attractive candidates for thin film photovoltaic applications for their tunable near-infrared absorption, multiple exciton generation effect and solution processability. In PbS CQD solar cells, however, insulating ligands such as 1,2-ethanedithiol (EDT) and 3-mercaptopropionic acid (MPA) are often used and do not contribute to optical absorbance, thereby limiting short-circuit current density (Jsc). To solve this issue, we chose CH3NH3PbI3 perovskite as a promising capping ligand of PbS CQDs by taking advantage of its long carrier diffusion length and complementary optical spectrum with PbS CQDs. In our work, a solid-state ligand exchange method instead of complicated solution-phase ligand exchange method is employed to obtain CH3NH3PbI3 capped PbS CQDs, which exhibit significantly improved optical and electrical properties than neat PbS CQDs. Saturated solution of CH3NH3PbI3 in acetonitrile enables to attain thick PbS films with complete ligand replacement in the layer-by-layer deposition process. In inverted solar cells of CH3NH3PbI3 capped PbS CQDs, CH3NH3PbI3 ligands can not only create a p/n heterojunction with PbS to facilitate charge separation, but also act as an energy relay between PbS and the TiO2 layer to form the cascade energy alignment and reduce the energy loss. Thus the optimal solar cell reaches an impressive Jsc of ~25 mA/cm2 and a power conversion efficiency (PCE) of 4.25%. Furthermore, upon the addition of EDT-capped PbS CQDs, the bilayer solar cells yields a remarkably enhanced PCE up to 5.28%, due to more balanced and efficient charge transport in the device.
J. Peng, Y. Chen, X. Zhang, A. Dong, Z. Liang, Solid-State Ligand-Exchange Fabrication of CH3NH3PbI3 Capped PbS Quantum Dot Solar Cells. Adv. Sci. 3, 1500432 (2016).
9:15 AM - ES1.1.02
Inverted Lead Acetate-Based Perovskite Solar Cells Exceeding 19% Efficiency through Crystallization Optimization and Interfacial Engineering
Yong Zhang 1 , Xianyong Zhou 1 , Chang Liu 1 , Weiguang Kong 1 , Chun Cheng 1 , Baomin Xu 1 Show Abstract
1 , South University of Science and Technology of China, Shenzhen, Guangdong, China
Hybrid organic-inorganic perovskite materials are now attracting more and more attention as the very promising candidate for the next generation low cost and high efficiency solar cell technology. The certified power conversion efficiency (PCE) of the perovskite solar cells (PSCs) rapidly increased from 3.8% to 22.1% in the past several years. The traditional lead source used in organic-inorganic perovskite precursor solution is halide lead such as PbI2 or PbCl2. However, some complex fabrication processes like anti-solvent method, two-step solution method or long time annealing is needed to convert lead iodide (PbI2) or lead chloride (PbCl2)-based precursor solution into good perovskite film. Lead acetate (PbAc2) is the most potential material to replace the halide lead because of the simple fabrication process and short annealing time to form high quality film. Furthermore, there is still plenty of room to improve the efficiency of PbAc2-based PSCs. Here, we present two simple approaches: crystallization optimization and controlled interfacial engineering. The crystallization of the perovskite film was controlled through the pre-treatment of the substrate and the precursor solvent. The optimized perovskite films were obtained by suitable temperature treatment, and as a result, the PbAc2-based PSCs achieved the PCE of 18.2% for 0.1 cm2 active area and 8.8% efficiency for large active area (2 cm2) devices. Moreover, a thin ionic liquid layer was introduced to modify the PEDOT:PSS hole transporting layer. The introduction of ionic liquid enhanced the charge transportation between the perovskite film and PEDOT:PSS layer. The device with optimized crystallization and controlled interfacial engineering delivered a champion PCE of 19.2% for 0.1 cm2 active area, which also exhibited no hysteresis under the scanning conditions.
9:30 AM - *ES1.1.03
(How) Can Halide Perovskites Impact PV
David Cahen 1 Show Abstract
1 , Weizmann Inst of Science, Rehovot Israel
The development of PV has seen quite a few alternatives (to c-Si), but only few are still with us, and even fewer have really impacted PV’s role as a more sustainable source of electrical power than fossil fuel-based generation. By looking for ways to put Halide Perovskite(HaP) cells in perspective with respect to other PV cells, we can suggest issues, both fundamental scientific and more practical development ones, that can be important for allowing HaP-based PV to influence the world electrical energy scene. These include real, perceived or imagined characteristics of the materials. At the meeting I will discuss these issues, with some emphasis on the low recombination rate (à high photovoltage), one of the more attractive features of HaP-based PV.
Work done with Gary Hodes
Support: Israel National Nano-initiative, Weizmann Institute of Science's Alternative sustainable Energy Research Initiative; Israel Ministry of Science.
10:00 AM - *ES1.1.04
Advanced Materials and Process for Facilitating Commercialization of Perovskite Solar Cells
Hyun Suk Jung 1 Show Abstract
1 , Sungkyunkwan Univ, Suwon Korea (the Republic of)
All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 22% and further improvements are expected up to 25%. These novel organometal halide perovskite absorbers which possess exceptionally strong and broad light absorption enable to approach the performances of the best thin film technologies. To commercialize these great solar cells, there are many bottlenecks such as long term stability, large scale fabrication process, and environmental issues.
In this presentation, we introduce our recent efforts to facilitate commercialization of perovskite solar cells. For examples, we introduce a recycling technology of perovskite solar cells, which will facilitate the commercialization as well as solve the environmental issues of perovskite solar cells. Moreover, Br-concentration gradient perovskite materials were realized by using HBr treatment of perovskite materials. The enhancement in hole extraction was verified from measurement of photoluminescence spectroscopy. Also, we are going to discuss about stability issue of perovskite materials regarding charge generation and extraction.
10:30 AM - ES1.1.05
In Situ Methylammonium Lead Halide Perovskite Growth—A Novel Approach for Solar Energy Technology
Muge Acik 1 , Yang Ren 1 , Fangmin Guo 1 , Todd Alam 4 , Byeongdu Lee 1 , Richard Rosenberg 1 , Alper Kinaci 1 , Benjamin Diroll 1 , Guiliang Xu 1 , Richard Schaller 1 5 , Maria Chan 1 , Saw-Wai Hla 1 3 , Seth Darling 1 2 Show Abstract
1 , Argonne National Laboratory, Lemont, Illinois, United States, 4 , Sandia National Laboratory, Albuquerque, New Mexico, United States, 5 , Northwestern University, Evanston, Illinois, United States, 3 , Ohio University, Athens, Ohio, United States, 2 , University of Chicago, Chicago, Illinois, United States
We introduce a one-step solution processing technique to facilitate photovoltaics commercialization – in situ perovskite polycrystal formation via substrate-free growth to produce micron to nano scale (< 500 nm), redispersable methylammonium lead halide crystals (CH3NH3Pbl3, CH3NH3PbBr3, CH3NH3PbCl3 and their mixed halides). Herein, an in situ solution-assisted preparation technique will be described that differs from conventional perovskite growth methods (i.e. one-step or two-step approach in DMF, followed by a hot-plate annealing). As a substrate-free approach, crystal pre-growth eliminates annealing and provides large-area deposition of crystals at room temperature with good film uniformity. This process is a temperature-assisted in situ crystallization method based on varying experimental conditions such as temperature, time, solution concentration and choice of solvent. Controlled homogeneous crystal growth is achieved by an immediate crystallization in solution upon mixing precursors (methylammonium iodide/bromide/chloride and lead (II) iodide/bromide/ chloride) in alcohols (methyl, ethyl, isopropyl, 1-butyl and 2-butyl) or in toluene through a nucleophilic substitution reaction at the solvent boiling points, followed by direct precipitation of the perovskite material.
Our solution growth technique results in dispersive perovskite crystals derived from polar protic alcohols or non-polar toluene as solvents not only eliminates deposition of a film onto a substrate and avoids heating to induce crystallization on the substrate, but also improves surface coverage of the films of the perovskite crystals and shows improvement in air/moisture stability (<1 month for the mixed halides and <2 months for single halide perovskites, tested in a fume hood at ~20°C under varying laboratory humidity level) as well as thermal stability in argon (~150°C for CH3NH3PbCl3, ~ 200°C for CH3NH3Pbl3 and ~300°C for CH3NH3PbBr3) in their dry powder form. The use of a variety of solvents is advantageous over conventional high boiling point solvents such as DMF. The resulting perovskite material has been found redispersable in polar aprotic solvents such as acetonitrile, hexane, or in acetone and toluene, which was extensively characterized by in situ techniques such as high energy synchrotron XRD, wide angle x-ray scattering (WAXS), Fourier transform infrared (FTIR) in transmission/reflection geometry (ATR, %Reflection), UV-Vis-NIR (%Reflection), and micro Raman spectroscopy. In situ FTIR and Raman spectra were combined with thermal annealing experiments, run at 20-400°C in argon/air, explained by first principles calculations. We also performed solid state 1H, 13C, 207Pb –MAS NMR, steady-state/time-resolved photoluminescence measurements, XPS, TGA, AFM, and SEM. (1) M. Acik et al. (2016) in preparation. (2) M. Acik et al. J. Mater. Chem. (2016) A 4 (17), 6185. (3) Gong et al. Energy Environ. Sci. 8 (2015) 1953. (4) Yue et al. Solar Energy 105 (2014) 669.
Use of the Center for Nanoscale Materials was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The abstract has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. Office of Science User Facility under Contract No. DE-AC02-06CH11357. M.A. also acknowledges support from the Joseph Katz Named Fellowship at Argonne National Laboratory.
11:15 AM - *ES1.1.06
Efficient and Stable Perovskite Solar Cells and Modules
Liyuan Han 1 , Luis Ono 1 Show Abstract
1 , NIMS, Tsukuba Japan
Perovskite solar cell (PSC) unprecedentedly developed in recent years due to its excellent photovoltaic performance and simple solution processing method. This time we introduce our main achievements obtained from inverted PSC devices with working area over one centimetre square. Firstly, reproducibility of device performance was improved through controlling the morphology and uniformity of perovskite layer and charge extraction layers in the solar cells. The thick charge extraction layers with high conductivity, such as NiO and TiO2 heavily doped with Mg2+, Li+ and Nb5+, were used to reduce pinhole of the film and increase the long-term stability of device.1 Secondly, we developed efficient inverted-structure with a perovskite-fullerene graded heterojunction (GHJ), which is featured with a gradient distribution of electron accepting material in the light absorption perovskite layer. This structure is found capable of enhancing the PCE of inverted structured PSCs as it improves the photoelectron collection and reduces recombination loss, especially for the formamidinium (FA) cation based perovskites that have superior spectra response and thermal stability. The conformal fullerene coating on perovskite during the GHJ deposition facilitates a full coverage of fullerene with reduced layer thickness, thus minimize the resistive loss in larger size devices. Though these efforts, we have successfully achieved certified efficiency of 18.2% based on a cell with an aperture area larger than one centimetre square.2 Furthermore, design of the modules and the cost simulation of PSCs module were also introduced. The costs of modules are found to be only one third of that of commercial silicon solar cells.3
(1) W. Chen, et al., Science, 350, 944 (2015).
(2) Y. Wu, et al., Nature Energy, 1, 16148 (2016).
(3) M. Cai, et al., Advanced Science, 2016, 1600269.
11:45 AM - *ES1.1.07
Fully Evaporated High Efficiency Perovskite Based Solar Cells
Lidon Gil-Escrig 1 , Cristina Momblona 1 , Jorge Avila 1 , Daniel Perez-del-Rey 1 , Michele Sessolo 1 , Henk Bolink 1 Show Abstract
1 , University of Valencia, Paterna Spain
Perovskite based solar cells, mostly employ solution processed perovskite layers. Evaporated methylammonium lead iodide perovskite layers have also been reported and been employed in solar cells. Our group has developed several perovskite based solar cells, using vacuum based perovskite preparation methods. These metal oxide free p-i-n type perovskite cells exhibit high power-conversion efficiencies. We have extended this work to fully evaporated perovskite devices reaching power conversion efficiencies as high as 20 % in a planar single junction device. We further will report on details related to the n-i-p and p-i-n devices as well as identifiy key properties from the stack. Avenues to further increase the device performance by using multiple cation perovskite prepared via sublimation will also be presented.
12:15 PM - ES1.1.08
Ligand-Facilitated Formation of Perovskite at Room Temperature—A Guideline from Theoretical and Experimental Study
Hong Zhang 1 , Jiaqi Cheng 1 , Francis Lin 2 , Dan Li 3 , Alex Jen 2 , Wallace Choy 1 Show Abstract
1 , University of Hong Kong, Hong Kong China, 2 Department of Materials Science & Engineering, University of Washington, Seattle, Washington, Washington, United States, 3 Key Laboratory of Luminescence and Optical Information, Beijing Jiao-tong University, Beijing China
Recently, organic-inorganic lead halide perovskites have been intensively studied for forming optoelectronic devices (e.g., solar cells, light-emitting diodes, and photodetectors) because of their low cost and high performance. While high-temperature sintering and annealing processes are typically used to prepare good-quality perovskites, thermal annealing for extended periods is known to cause perovskite decomposition, which degrades device performance, stability, and reproducibility. Therefore, it is highly desirable to develop room-temperature processed methods for controllably forming perovskite films.
In this work, we propose a room-temperature scheme of controllable ligand-assisted formation of perovskite films featuring large grain-sizes, and high crystallinity while being free of impurities. Different representative ligands with different features (molecular size, volatility, solubility, and reac-tivity) are experimentally investigated to unravel the ligand effects on the formation kinetics, morphology, and optoelec-tronic properties of perovskite. The mechanism of ligand-assisted perovskite formation is theoretically elucidated through the thermodynamics and chemical kinetics studies. With the experimental and theoretical studies, a selection rule for identifying ideal ligands for formation of high-quality perovskite films is established. This work offers a fundamental understanding of ligand effects on the formation of perovskite films for the future design of high-performance and low-cost perovskite-based optoelectronics.
12:30 PM - ES1.1.09
Hybrid Perovskite Thin Film Formation—An In Situ Investigation of Solvent Engineering and Its Implication on Microstructural and Morphological Control
Rahim Munir 1 , Arif Sheikh 1 , Ming-Chun Tang 1 , Jafar Khan 1 , Ruipeng Li 2 , Detlef Smilgies 2 , Aram Amassian 1 Show Abstract
1 , King Abdullah University of Science and Technology, Thuwal-Jeddah Saudi Arabia, 2 CHESS, Cornell, Ithaca, New York, United States
Organometallic lead halide perovskite material has gained high popularity among all other semiconductors because of its high performance in a variety of applications in solar cells, sensors, LED, detectors, etc. The ease of processing these materials through solution routes, such as spin-coating, blade-coating and spray coating makes them particularly attractive. Solvent engineering, where precursors are dissolved in a mixture of solvent and anti-solvent drip is applied during the coating process, has recently emerged as a critical step for controlling the microstructural and morphological outcome of ink drying and solidification and has been shown to produce pin-hole-free films with high power conversion efficiency, justifying its broad adoption across the field. This talk will describe our recent investigations into the crucial role of anti-solvent dripping on the solution-to-solid phase transformation of MAPbI3, FAPbI3 and FAxCs1-xPbI3 perovskite systems. To do so, we utilize a suite of in situ diagnostic probes including high speed optical microscopy, optical reflectance and absorbance, and grazing incidence wide angle x-ray scattering (GIWAXS), all performed during spin coating, to monitor the solution thinning behavior, changes in optical absorbance, and nucleation and growth of crystalline phases of the precursor and perovskite. Our investigations reveal that the choice of processing solvent, namely DMSO and GBL, and their ratios, strongly impact the effectiveness of the anti-solvent drip. Our time-resolved observations reveal the anti-solvent drip must be applied before the crystallization of the precursor solvates, which also depends upon the solvent mixture, placing additional importance on the timing of the drip in achieving optimal morphology and device performance reproducibility. The insight provided by in situ studies should improve perovskite thin film manufacturability in terms of solar cell performance, yield and reproducibility.
12:45 PM - ES1.1.10
All Laser Scribed Perovskite Solar Mini-Modules
Stefano Pisoni 1 , Lukas Bayer 2 , Fan Fu 1 , Klaus Zimmer 2 , Stephan Buecheler 1 , Ayodhya Tiwari 1 Show Abstract
1 , EMPA, Dubendorf Switzerland, 2 , Leibniz-Institut für Oberflächenmodifizierung e.V., Leipzig Germany
In the last few years, high efficiency perovskite solar cells of small area have been developed in research lab. However, in order to enable commercialization of this technology, it is pivotal to increase the device area and develop solar cell interconnection processes for making solar modules. For these reasons, we have developed laser scribing processes and monolithically connected perovskite mini-modules.
In upscaling of device area a drop in efficiency due to resistive losses is expected. Therefore, the dimensions of the serial interconnected single solar cells should be properly defined according to the sheet resistance of the transparent conducting oxide (TCO) layer. Moreover, the uniformity of the constituent layers and quality of interconnections must be taken into account to obtain high efficiency solar modules. In this work, we show a reproducible and scalable method to fabricate large-area, high quality perovskite films using a two-step deposition method which combines vacuum- and solution-based processes. Interconnection patterning is obtained entirely by laser scribing using picosecond laser pulses with a wavelength of 355 nm to minimize dead area losses between interconnected solar cells. Preliminary development of monolithically interconnected mini-modules of 6.73 cm2 aperture area has already yielded promising results with stabilized efficiencies up to 11%. Devices in planar heterojunction configuration were developed, avoiding the use of high-temperature processes for mesoporous scaffolds. The electron transport layer stack was grown by vacuum deposition techniques, ensuring a uniform coating for large area substrates. The low-temperature process is suitable for flexible plastic foils and roll-to-roll manufacturing. The paper would present results on upscaling of small area perovskite solar cells to mini-module sizes and discuss the challenges and prospects of laser scribing and large area deposition techniques for perovskite solar modules development on different substrates.
ES1.2: Device Stability, Electron and Hole Transport Layers
Monday PM, April 17, 2017
PCC North, 200 Level, Room 224 B
2:30 PM - *ES1.2.01
Lead Halide and Lead-Free Perovskite Solar Cells by Metal Oxide-Based Low Temperature Processes
Tsutomu Miyasaka 1 , Masashi Ikegami 1 , Ashish Kulkarni 1 , Trilok Singh 1 , Atsushi Kogo 1 Show Abstract
1 , Toin University of Yokohama, Yokohama Japan
Hybrid perovskite solar cell, reaching power conversion efficiency (PCE) above 22%, exert a maximal merit in cost reduction of manufacture by combining cheap materials with low process temperature, the latter leading to high speed production. Low temperature printing process (<120oC) can be applied to hybrid perovskite cells by using organic conductive materials (PEDOT, PCBM, etc.) and/or nanocrystalline SnO2, ZnO, and their composites for carrier transporting layers. With high voltage >1.1V, PCE of these cells can compete with sintered metal oxide (TiO2, etc.)-based perovskite cells on glass substrates. The printing process also meets fabrication of flexible cells on plastic substrates. SnO2 works as a good electron collector exhibiting durable and hysteresis-less photovoltaic performance, due to good interfacial connects at the junction with perovskite crystals by suppressing recombination. This indicates the quality of heterojunction interfaces is essential to high performing device. We showed that low temperature-based Al2O3/ZnO/SnO2 composite works as good collector of MAPbI3 with PCE>15% and high stability . On ZnO collector, FAPbI3 was found to be chemically more stable than MAPbI3, exhibiting PCE>16% . Chemically most stable TiO2 generally needs high temperature sintering process to prepare mesoporous layer. As an exception, brookite nanocrystal is capable of strong interparticle necking at temperature <120oC through dehydration condensation reaction that enables formation of dense uniform layer. Brookite-based plastic (ITO-PEN) film perovskite cell prepared on amorphous SnOx compact layer shows non-hysteretic performance with PCE 14% and high mechanical stability against bending .
Our best efficiencies of low-temperature based perovskite solar cell and triple-cation based cell, both made on TiO2 electron collectors, were 21.6% and 20.8%, respectively. Despite high efficiency of lead halide perovskite, continuous effort to explore lead-free materials is highly important. Lead-free halide perovskite solar cells can also be made on low-temperature prepared metal oxide collectors. We have fabricated Bi-based perovskite device on various metal oxide underlayers, which exhibited strong influence on the morphology of (CH3NH3)3Bi2I9 [4,5]. By interfacial engineering using organic additives, dendritic absorber layer was converted to flat uniform layer, leading to improvement in photovoltaic performance. All above experiments corroborate importance of the quality of metal oxide collector, which determines the quality of current-rectifying interfaces against recombination loss.
 J. Song, E. Zheng, X.-F. Wang, W. Tian, T. Miyasaka, Solar Ener. Mat. Solar Cells, 2016, 144, 623-630.
 J. Song, W. Hu, X.-F. Wang, G. Chen, W. Tian, and T. Miyasaka, J. Mater. Chem. A, 2016,4, 8435-8443.
 A. Kogo, M. Ikegami, and T. Miyasaka, Chem. Commun., 2016, 52, 8119-8122.
 T. Singh, A. Kulkarni, M. Ikegami, and T. Miyasaka, ACS Appl. Mater. Interfaces, 2016, 8, 14542-14547.
 A. Kulkarni, T. Singh, M. Ikegami, and T. Miyasaka, submitted.
3:00 PM - ES1.2.02
Defective TiO2 with High Photoconductive Gain for Efficient and Stable Planar Heterojunction Perovskite Solar Cells
Yanbo Li 1 2 , Jason Cooper 2 , Carolin Sutter-Fella 2 , Ali Javey 2 , Joel Ager 2 , Francesca Maria Toma 2 , Ian Sharp 2 Show Abstract
1 IFFS, University of Electronic Science and Technology of China, Chengdu, Sichuan, China, 2 JCAP, Lawrence Berkeley National Lab, Berkeley, California, United States
Planar heterojunction perovskite solar cells (PSCs) with both high efficiency and good stability under operating conditions remains a challenge. Here, we consider that the TiO2 electron transfer layer (ETL) is illuminated during operation of PSCs and show that the photoexcited state properties of the compact ETLs play critical roles in defining device performance in terms of efficiency and stability. Both the photoconductivity and photocatalytic activity of TiO2 are greatly affected by deep level trap states associated with native point defects. In this work, we have engineered a defective TiO2 thin film containing such hole trap states and used it as the ETL for planar heterojunction PSCs. Photoconductive measurements show that the defective TiO2 thin film has an internal gain higher than 103 at a small bias of 0.5 V, which is attributed to the minority carrier trapping mechanism in the film. By coupling the highly photoconductive TiO2 ETL with a high quality perovskite light absorber synthesized using a low-pressure vapor annealing process, a highly efficient planar heterojunction PSC with relatively small hysteresis is achieved. The maximum PCEs under reverse scan, forward scan, and steady-state are 19.0%, 17.1%, and 17.6%, respectively. Moreover, the stability of the planar heterojunction PSC is greatly improved by using defective TiO2 as the ETL. TiO2 is known to be an effective UV photocatalyst for oxidizing organic materials and the hybrid perovskite can be photocatalytically degraded under UV illumination, which typically leads to poor stability for the PSCs. The incorporation of hole-trap states in the TiO2 ETL reduces its activity for photocatalytic oxidation. As a result, the stability of fabricated planar heterojunction PSCs is greatly improved and we show, for the first time, steady-state PCE greater than 15.4% during continuous operation for 100 h. These results demonstrate that engineering defects in the TiO2 ETL is a promising way to improve the efficiency and stability of planar heterojunction PSCs.
3:15 PM - ES1.2.03
Roles of Hole Transport Layer Additives in Perovskite Solar Cell
Shen Wang 1 , Mahsa Sina 1 , Pritesh Parikh 1 , Y. Shirley Meng 1 Show Abstract
1 , University of California, San Diego, La Jolla, California, United States
As an emerging photovoltaic device with commercial potential, hybrid organic-inorganic perovskite solar cells (PSCs) have developed rapidly in the recent years. With a certified 22.1% power conversion efficiency, compatibility with flexible substrates and low fabrication energy consumption, PSCs are attracting enormous interest in both the academic and industrial field. Although the charge transfer and recombination mechanisms are different for solid-state dye-sensitized solar cells (ssDSSCs) and perovskite solar cells, similar hole transport materials and additives are applied in both of them. For instance, bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) and 4-tert-Butylpyridine (tBP) are both used in PSCs and ss-DSSCs as the hole transport layer additives. However, the only difference is indicated in their functions. In ssDSSCs, tBP is the charge recombination inhibitor while LiTFSI is the dopant.
This research is characterized the roles of tBP and LiTFSI in PSCs. A spectrum-dependent HTL oxidation mechanism in perovskite was proposed which in association with LiTFSI. On the other hand, based on focused ion beam (FIB) and bright filed transimission electron microscopy (BF-TEM), it has been discovered that tBP controls the morphology of HTL in PSCs. The study also indicates that, the existence of tBP can dramatically reduce the hygroscopicity of HTL and enhance the stability of PSCs. Atom probe tomography was applied for the first time in this field to illustrate this phenomenon. Moreover, this research has concluded that LiTFSI and tBP can form a series of complexes. These complexes improve the device performance and also slow down the further degradation from perovskite to its precursors.
1 Wang, S., Yuan, W., & Meng, Y. S. (2015). Spectrum-Dependent Spiro-OMeTAD Oxidization Mechanism in Perovskite Solar Cells. ACS applied materials & interfaces, 7(44), 24791-24798.
2 Wang, S., Sina, M., Parikh, P., Uekert, T., Shahbazian, B., Devaraj, A., & Meng, Y. S. (2016). Role of 4-tert-Butylpyridine as a Hole Transport Layer Morphological Controller in Perovskite Solar Cells. Nano Letters, 16(9), 5594-5600.
3:30 PM - ES1.2.04
Accelerated Stability Testing of Perovskite Photovoltaic Materials Reveals Dependence on the Halide Composition and Synthesis Details
Ravi Misra 3 , Laura Ciammaruchi 1 , Sigalit Aharon 3 , Baili Li 1 , Dmitry Mogilyanski 2 , Lioz Etgar 3 , Eugene Katz 1 2 , Iris Visoly-Fisher 1 2 Show Abstract
3 Casali Center for Applied Chemistry, The Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem Israel, 1 Department of Solar Energy, Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion Israel, 2 Ilse Katz Institute of Nano-Science and Technology, Ben-Gurion University of the Negev, Be'er Sheva Israel
The greatest challenge facing the development of organic and perovskite photovoltaics is combining high efficiency and long-term stability. We recently demonstrated the first realization of stability testing methodology using concentrated sunlight that allows independent control of light intensity, the sample temperature and environment during the exposure. Accelerated photo-stability testing of hybrid perovskite MAPbX3 films (X = I or Br) by exposure to 100 suns showed that the evolution of light absorption and the corresponding structural modifications were dependent on the type of halide ion and the sample temperature. The degradation in absorption of MAPbI3 films after exposure at elevated sample temperature (~45-55oC), due to decomposition of the hybrid perovskite material, was documented, while no photobleaching or decomposition of MAPbBr3 films were observed after exposure to similar stress conditions. This improved stability was related to differences in Br-related bond strengths and in the perovskites' crystalline forms. The stability of pure MAPbI3 and MAPbBr3 films was found to be superior to that of mixed halide compositions MAPb(I1-xBrx)3, possibly due to stressing its crystal structure, inducing more structural defects and/or grain boundaries compared to pure halide perovskites. Hence, the cause for accelerated degradation may be the increased defect density rather than the chemical composition of the perovskite materials. Furthermore, the synthesis sequence of the Perovskite deposition process was found to affect its stability, due to the effect of PbI2 residue in the film.
 I. Visoly-Fisher, A. Mescheloff, M. Gabay, C. Bounioux, L. Zeiri, M. Sansotera, A. E. Goryachev, A. Braun, Y. Galagan, E.A. Katz, Sol. Ener. Mater. & Sol. Cells 134 (2015), 99–107.
 R. K. Misra, S. Aharon, B. Li, D. Mogilyanski, I. Visoly-Fisher, L. Etgar, E. A. Katz, J. Phys. Chem. Lett. 6 (2015), 326−330.
 R. K. Misra, L. Ciammaruchi, S. Aharon, D. Mogilyanski, L. Etgar, I. Visoly-Fisher, E. A. Katz, ., ChemSusChem 9 (2016), 2572 – 2577.
 In prep.
3:45 PM - ES1.2.05
Thermal Degradation of CH3NH3PbI3 Perovskite into NH3 and CH3I Gases Observed by Coupled Thermogravimetry–Mass Spectrometry Analysis
Emilio Juarez-Perez 1 , Zafer Hawash 1 , Sonia Raga 1 , Luis Ono 1 , Yabing Qi 1 Show Abstract
1 Energy Materials and Surface Sciences Unit (EMSS), Okinawa Institute of Science and Technology Graduate University (OIST), Onna-son Japan
In the past few years, we have all witnessed the unprecedented zeal for the rapid growth of organometal halide perovskite solar cell field. The tremendous efforts devoted to device fabrication and optimization have led to PCEs exceeding 20%, which gives perovskite solar cells the competitive advantage over many other well-known solar technologies. On the other hand, some challenges remain with the lifetime to be the key. At present, even the most long-lasting perovskite solar cells can retain stable PCEs up to a few thousands of hours, which is way behind for example silicon cells. To further advance perovskite solar cells, we must overcome/mitigate the degradation issue. For this reason, a thorough detailed understanding for perovskite solar cell degradation processes becomes an imperative first step.
Thermal gravimetric and differential thermal analysis (TG-DTA) coupled with quadrupole mass spectrometry (MS) instrumentation and first principles calculations were employed to elucidate the chemical nature of released gases during the thermal decomposition of CH3NH3PbI3. Contrarily to the common wisdom that CH3NH3PbI3 is decomposed into CH3NH2 and HI, the major gases were methyliodide (CH3I) and ammonia (NH3). We anticipate our finding will provide new insights for further formulations of the perovskite active material and device design that can prevent the methylammonium decomposition and thus increase the long-term stability of perovsktie-based optoelectronic devices.
 E. J. Juarez-Perez, Z. Hawash, S. R. Raga, L. K. Ono, Y. B. Qi, Thermal degradation of CH3NH3PbI3 perovskite into NH3 and CH3I gases observed by coupled thermogravimetry - mass spectrometry analysis, Energy Environ. Sci. 2016, 9, 3406-3410.
4:30 PM - *ES1.2.06
Issues on Efficiency and Stability of Perovskite Solar Cells
Shihe Yang 1 Show Abstract
1 , Hong Kong University of Science and Technology, Kowloon Hong Kong
Hybrid organic/inorganic perovskite solar cells have emerged as among the most competitive photovoltaic technologies of the future thanks to their superb and rapidly improving power conversion efficiencies (PCEs). For realistic deployment of the perovskite photovoltaic technology in large scale, however, device stability has become more and more important issue of the day. This talk will present our recent results on (1) the relationship between device stability and ion movement of the perovskite layer; 2) the use of NiO and carbon nanostructures for efficient hole extraction and enhanced device stability; and 3) the development of perovskite and interface engineering techniques for improving both efficiency and stability. Implications of these results on the future development of perovskite solar cells will be discussed.
5:00 PM - ES1.2.07
Performance Enhancement of Perovskite Solar Cells with SnO2 Electron Transport Layer
Guojia Fang 1 , Weijun Ke 2 , Guang Yang 1 , Liangbin Xiong 1 , Xiaolu Zheng 1 , Junjie Ma 1 , Zhiliang Chen 1 , Cong Chen 1 Show Abstract
1 , Wuhan University, Wuhan, Hubei, China, 2 , Northwestern University, Chicago, Illinois, United States
We report perovskite solar cells with nano-SnO2 as electron-transport layers (ETLs), which outperform cells using TiO2 ETLs in several ways: higher open-circuit voltage (Voc), power conversion efficiencie, short-circuit current and fill factor. These properties improvements are attributed to the better properties of SnO2 as compared to TiO2, such as better optical transmission properties, wider band gap, better hole-blocking effect and higher electron mobility. We demonstrate that low-temperature solution processed nanocrystalline SnO2 can be an excellent alternative ETL material for efficient perovskite solar cells. Also, we demonstrate that SnO2 and fullerenes can work cooperatively to further boost the performance of perovskite solar cells. The SnO2 layer blocks holes effectively; whereas, the ultra-thin fullerenes promote electron transfer and passivate traps and defects at the SnO2/perovskite interface. Based on SnO2 electron transport layer, we also demonstrate a one-step solution process for perovskite film deposition and demonstrate that adding a small amount of lead thiocyanate (Pb(SCN)2) in the perovskite precursor can significantly increase the grain size and crystalline quality of perovskite thin films. Using conventional reverse and forward voltage scanning, PCEs of 19.45% and 18.53% were obtained, respectively. The simple low-temperature process is compatible with the future roll-to-roll manufacturing of low-cost perovskite solar cells on flexible substrates.
5:15 PM - ES1.2.09
Dense Silica Barrier Films for Improved Efficiency and Stability of Perovskite Solar Cells Deposited in Ambient Air
Nicholas Rolston 1 , Adam Printz 1 , Siming Dong 1 , Brian Watson 1 , Reinhold Dauskardt 1 Show Abstract
1 , Stanford University, Stanford, California, United States
Hybrid perovskites hold tremendous promise for next-generation solar cells, more than any other recently developed low-cost active PV material. However, their extreme moisture sensitivity, thermal instability, and mechanical fragility limit their viability as a reliable solar technology. It is therefore imperative that the thermomechanical properties of perovskite solar cells are improved to realize commercialization.
We address all three of these degradation pathways by atmospheric plasma deposition of tetraethoxysilane (TEOS) to produce a submicron dense silica barrier film on top of a completed perovskite device. This scalable, high throughput process allows for solvent-free deposition at low temperature without damaging the perovskite in any way. Surprisingly, we found that the efficiency of devices increased from 15.0% to 15.7% with improved Voc and FF after depositing the barrier film. We attribute the increased Voc to improved interfaces or enhanced crystallinity of the perovskite from the heat of the plasma and the improved FF to enhanced charge transport from the plasma gas oxidizing the PTAA. The barrier film improved the moisture stability of perovskite devices by several orders of magnitude, allowing for operation in 85% R.H. environments without any degradation. Also, the thermal stability of the perovskite devices was greatly enhanced. We demonstrated this by laminating ethylene-vinyl acetate (EVA), the industrial standard commercial silicon encapsulant, on the devices. EVA cures at 140°C for 20 minutes, a temperature which degrades perovskite without the barrier film. Finally, we showed the barrier film is compatible with flexible devices by depositing on perovskite devices fabricated on PET substrates and performing mechanical bending cycles with varying bending radii. Optical microscope images revealed the barrier film did not crack or deform after 1,000 cycles with a bending radius of 1 cm, indicating the robust mechanical properties of the ultrathin silica.
5:30 PM - ES1.2.10
Self-Encapsulating Air-Resilient Semitransparent Perovskite Solar Cells with Superior Thermal Stability Beyond 2000 h
Kai Brinkmann 1 , Jie Zhao 1 2 , Ting Hu 1 2 , Neda Pourdavoud 1 , Tobias Gahlmann 1 , Ralf Heiderhoff 1 , Andreas Polywka 1 , Yiwang Chen 2 , Patrick Goerrn 1 , Thomas Riedl 1 Show Abstract
1 , Bergische Universität Wuppertal, Wuppertal Germany, 2 Institute of Polymers, College of Chemistry, Nanchang China
Semitransparent organo-lead halide perovskite based solar cells (PSCs) are showing great promise for applications in tandem devices and for building-integration. For a serious application, it is crucial to face the severe stability concerns. E.g. methyl-ammonium lead iodide (MAPbI3) has been shown to decompose when exposed to moisture or heat. This limits the use of ITO as semitransparent electrode on top of the device, as ITO requires high temperature post processing (>300°C) to become highly conductive and transparent. An alternative concept of a semitransparent electrode is based on ultra-thin metal layers. Unfortunately, ultra-thin metal layers are especially sensitive to the chemical attack by halide containing decomposition products of perovskites [2,3].
Here, we demonstrate outstandingly robust PSCs with semi-transparent top electrodes based on SnOx/Ag/SnOx. As a key, the ultra-thin Ag layer (7 nm) is sandwiched between SnOx grown by low-temperature atomic layer deposition (ALD). We have shown that these SnOx layers not only provide outstanding permeation barrier properties, but they are also highly transparent and electrically conductive . Thus the SnOx layers can be placed inside the device and electrically interface the metal layer with the photo-active material. Even more importantly, the impermeable SnOx underneath the thin metal electrode is the key to the applicability of an additional ALD thin film encapsulation on top of the electrode. In the absence of the SnOx layer, ALD encapsulation is evidenced to inflict notable degradation of the device performance. We demonstrate semi-transparent PSCs with efficiencies higher than 11 % with about 70% average transmittance in the NIR (l > 800 nm) and 17% in the visible region (l = 500-750 nm). Most importantly, the devices reveal an astonishing stability over more than 2000 h regardless if they are exposed to ambient atmosphere (50 % RH) or elevated temperature (60○C in N2).
The presented SnOx/metal/SnOx semi-transparent electrode architecture is generally applicable for semi-transparent PSCs with various active and electrode materials. Given the fact that ALD has been shown to be roll-to-roll compatible, our results provide a significant step towards the commercialization of semitransparent perovskite solar cells.
 C. D. Bailie et al., MRS Bulletin, 2015, 681.
 Y. Kato et al., Adv. Mater. Interf. 2015, 2, 1500195.
 K. Brinkmann et al., Nat. Comms. (in revision).
 A. Behrendt et al., Adv. Mater. 2015, 27, 5961.
Yabing Qi, Okinawa Institute of Science and Technology
Wei Huang, Nanjing Tech University
Nam-Gyu Park, Sungkyunkwan University
Kai Zhu, National Renewable Energy Laboratory
Applied Physics Letters | AIP Publishing
The Journal of Physical Chemistry Letters | ACS Publications
National Renewable Energy Laboratory
Nature Energy | Springer Nature
Science Magazine| AAAS
Wiley VCH Verlag GmbH &
ES1.3: Micro-Structure, Defects and Traps
Tuesday AM, April 18, 2017
PCC North, 200 Level, Room 224 B
11:30 AM - *ES1.3.01
How Much Do We Know about Perovskite
Jinsong Huang 1 Show Abstract
1 , University of Nebraska–Lincoln, Lincoln, Nebraska, United States
In this talk, I will present our progress in understanding the unique optoelectronic properties and mechanical properties of hybrid perovskites. Photon recycling, i.e., the iterative self-absorption and re-emission by the photo-active layer itself, has been speculated to contribute to the high open circuit voltage (Voc) in several types of high efficiency solar cells. For organic–inorganic halide perovskites that have yielded highly efficient photovoltaic devices, however, it remains unclear whether photon recycling effect is significant enough to improve the solar cell efficiency. Here, we quantitatively evaluate the photon recycling efficiency in hybrid perovskite with their single crystals by measuring the ratio of the re-emitted photons to the initially excited photons, which is realized by modulating their polarization to differentiate them. Another fundamental question is whether the perovskite material is ferroelectric. I will present our new discovery of unique electromechanical properties of perovskite.
12:00 PM - *ES1.3.02
Spiro-MeOTAD Hole Transport Layer in Perovskite-Based Solar Cells
Luis Ono 1 , Zafer Hawash 1 , Sonia Raga 1 , Emilio Juarez-Perez 1 , Matthew Leyden 1 , Yuichi Kato 1 , Mikas Remeika 1 , Shenghao Wang 1 , Michael Lee 1 , Andrew Winchester 1 , Atsushi Gabe 1 , Yan Jiang 1 , Yabing Qi 1 , Han Cheh 1 Show Abstract
1 , Okinawa Institute of Science and Technology, Okinawa Japan
In organic-inorganic hybrid perovskite solar cells, optimization of hole transport materials (HTMs) is important for enhancing solar power conversion efficiency and improving stability. At OIST, a team of researchers in the Energy Materials and Surface Sciences Unit has been making concerted efforts to study 2,2’,7,7’-tetrakis[N,N-di-(4-methoxyphenyl)amino]-9,9’-spirobifluorene (spiro-MeOTAD), which is the most widely used HTM in perovskite solar cells [1-7]. In this talk, we will present our latest understanding of fundamental interactions between Li-bis(trifluoromethanesulfonyl)-imide (LiTFSI), 4-tert-butylpyridine (t-BP) and spiro-MeOTAD. Also, we will show how gas exposure (e.g., exposure to O2, H2O, N2) influences electronic structures and conductivity of such HTM films. In addition, we will propose further strategies to improve perovskite solar cell performance and stability [4,6].
 E.J. Juarez-Perez, M.R. Leyden, S. Wang, L.K. Ono, Z. Hawash, Y.B. Qi*, Chem. Mater. 28 (2016) 5702.
 Z. Hawash, L.K. Ono, Y.B. Qi*, Adv. Mater. Interfaces 3 (2016) 1600117.
 Z. Hawash, L.K. Ono, S.R. Raga, M.V. Lee, Y.B. Qi*, Chem. Mater. 27 (2015) 562.
 L.K. Ono+, S.R. Raga+, M. Remeika, A.J. Winchester, A. Gabe, Y.B. Qi*, J. Mater. Chem. A 3 (2015) 15451 (+These authors contributed equally)
 Y. Kato, L.K. Ono, M.V. Lee, S. Wang, S.R. Raga, Y.B. Qi*, Adv. Mater. Interfaces 2 (2015) 1500195.
 M.C. Jung, S.R. Raga, L.K. Ono, Y.B. Qi*, Sci. Rep. 5 (2015) 9863.
 L.K. Ono, P. Schulz, J.J. Endres, G.O. Nikiforov, Y. Kato, A. Kahn, Y.B. Qi*, J. Phys. Chem. Lett. 5 (2014) 1374.
12:30 PM - *ES1.3.03
Controlling Surface Trap Density in Hybrid Perovskite Single Crystals and Thin Films
Maria Antonietta Loi 1 Show Abstract
1 , University of Groningen, Groningen Netherlands
Remarkable physical properties such as tunable direct bandgap, high absorption coefficient, long carrier diffusion length and low temperature processability make hybrid perovskites ideal for optoelectronic device applications. Recently, also the low density of trap states has been argued to be one of the qualities giving to hybrid perovskites an edge over other materials.
In this presentation I will report about the unusually low surface recombination velocity (SRV) of 4 cm/s (corresponding to a surface trap state density of 108 cm2) in methylammonium-lead tribromide (MAPbBr3). By combining one- and two-photons excitation I will demonstrate, that the surface recombination rate (or surface trap state density) can be fully and reversibly controlled by the physisorption of oxygen and/or water molecules, leading to a photoluminescence intensity modulation of over two orders of magnitude. In addition, a consistent modulation of the transport properties in single crystal devices is evidenced. These findings not only highlight the importance of environmental conditions on the investigation and fabrication of high quality, perovskite-based devices, but offer also a new potential application of these materials for highly sensitive gas sensors.
ES1.4: Characterization, Interface and Modeling
Tuesday PM, April 18, 2017
PCC North, 200 Level, Room 224 B
2:30 PM - *ES1.4.01
Interface and Intermediate Phases Engineering for Achieving Efficient Perovskite Solar Cells
Yang Yang 1 , Lijian Zuo 1 , Jin-wook Lee 1 Show Abstract
1 , University of California, Los Angeles, Los Angeles, California, United States
The interfacial properties and morphology are two essential factors governing the device performance of perovskite solar cells. The ionic nature enabled the perovskite films with exceptional optoelectronic properties, and also make specific optimization strategies different from other PV techniques, e.g. the organic solar cells, and more. In this work, we investigate the role of interfacial chemical interactions for perovskite solar cells, and conclude that the chemical interactions at the interface between the perovskite and electrode dominates the interfacial properties instead of the energy level alignment. Perovskite solar cell with champion efficiency of 18.8% is obtained by modifying the interfacial chemical interactions, which constitute 10% improvement compared to that without modification.
On the other hand, we developed a novel method of vapor-induced-intermediate-phases (VIP) to control the perovskite morphology for extremely high solar energy conversion efficiency. In transition from the precursor to perovskite structure, intermediate phases have demonstrated to be highly important in morphological evolution, but have been limited in the past by both processing methods (one step solution process with DMSO additives) and intermediate phase species (PbI2-MAI-DMSO). Our work reports, for the first time, the generation of various intermediate phases by exposing the precursor films to different saturated solvent vapor atmospheres. With this method, we constructed different intermediate phases to facilitate perovskite film formation. Thereafter, high quality perovskite films were obtained, and a champion power conversion efficiency of 19.2% was achieved as one of the highest planar junction perovskite solar cells reported in literature.
3:00 PM - *ES1.4.02
Electronic Characterizations of Perovskite PVs and Their Interpretation via Numerical Simulations
Kenjiro Miyano 1 , Dhruba Khadka 1 , Masatoshi Yanagida 1 , Yasuhiro Shirai 1 Show Abstract
1 , NIMS, Tsukuba Japan
We have previously shown (1) that the electronic properties of hysteresis-free perovskite PVs are well represented in terms of the conventional inorganic semiconductors. They are essentially p-i-n diodes with wide i-region and akin to well-studied inorganic thin film PVs by quantitative comparison of electronic properties (J/V and impedance spectroscopy). In order for the perovskite PVs to be a viable choice for the market, a systematic approach for the device improvement is essential. We extended our approach borrowed from the thin-film PV field for better understanding the difference in the device performance. We will discuss the results of electronic measurements (especially their temperature dependence) performed with samples in variable conditions. We will examine the different electronic characteristics depending on the sample preparation, resulting in varying performances. We will also discuss the change in a device before and after the degradation. The change in the electronic characteristics will be compared with numerical simulations and microscopic origin of the different behavior will be inferred.
(1) Appl. Phys. Lett. 106, 093903 (2015), Acc. Chem. Res. 49, 303 (2016)
3:30 PM - ES1.4.03
Electronic Structure of the Interfaces between the Perovskite Absorber Layer and the Surrounding Transport Layers in Perovskite Solar Cells
Carolin Wittich 2 , Kerstin Lakus-Wollny 1 , Eric Mankel 1 , Thomas Mayer 1 , Hans-Joachim Kleebe 2 , Wolfram Jaegermann 1 Show Abstract
2 Geomaterialscience, Technische Universität Darmstadt, Darmstadt, Hessen, Germany, 1 Surface Science, Technische Universität Darmstadt, Darmstadt Germany
The interface properties in a perovskite solar cell have a large impact on carrier transport and cell performance. Particularly, the electronic structure of the interfaces between transport layers and the perovskite layer is therefore of great interest.
In this work, we used in situ X-ray photoelectron spectroscopy (XPS/UPS) to investigate the electronic interface properties between the titanium dioxide electron transport layer and the CH3NH3PbX3 perovskite absorber layer. Therefore, we stepwise deposited thin perovskite layers on differently prepared and cleaned TiO2 substrates by a physical vapor deposition process (PVD). The vacuum based PVD process consists of lead halogenide (PbX2) and methylammonium iodide deposition. After each evaporation step photoemission spectra of the relevant core level lines and the valence region were taken. The electronic band alignment was determined and interface band diagrams were drawn. The experimental data show that the interface properties strongly depend on the electronic surface conditions of the buffer layer. Additionally, the interface between the absorber and the hole transport layer (Spiro-OMeTAD) was analyzed in the same way.
Furthermore, the perovskite layer and the influence of different deposition parameters such as pressure and substrate temperature on morphology and composition were studied using XPS, X-ray diffraction and scanning electron microscopy (SEM). The measurements show that the resulting layer thicknesses and the electronic properties strongly depend on the deposition parameters. The deposition conditions determine the electronic, chemical and morphologic interface structure of the perovskite and the surrounding transport layers.
3:45 PM - ES1.4.04
Highly Efficient Perovskite Modules Resulted from Improved Perovskite Layer Formation and Interface Engineering
Weiming Qiu 1 , Aniruddha Ray 1 , Tamara Merckx 1 , Joao Bastos 1 , Lucija Rakocevic 1 , Manoj Jaysankar 1 , Robert Gehlhaar 1 , David Cheyns 1 , Jef Poortmans 1 , Paul Heremans 1 Show Abstract
1 , imec, Heverlee Belgium
Impressive progress has been made in perovskite photovoltaics during the past few years, boosting the power conversion efficiency (PCE) of small area perovskite solar cells up to 22.1%. This value is almost identical to that of the commercialized counterparts such as CdTe or CIGS based solar cells. However, the PCEs of perovskite modules, especially those with large areas, still lag behind those of small area devices. In this contribution, we present our recent progress on improving the perovskite layer formation and interface engineering, in order to get highly efficient perovskite solar modules. We will also show the fabrication of perovskite modules with high geometrical fill factor.
First of all, we developed a new precursor combination containing Pb(CH3CO2)2×3H2O, PbCl2, and CH3NH3I, which enabled us to fabricate pinhole-free CH3NH3PbI3-xClx layers on a large area.1 Spin-coated small area (0.13 cm2) perovskite solar cells reached a PCE of 17%, using a planar device structure of ITO/TiO2/perovskite/Spiro-OMeTAD/Au. By virtue of the uniformity of the perovskite film, perovskite solar modules with aperture areas of 4 cm2, 16 cm2, and 156 cm2 were obtained, showing aperture PCEs of 13.6%, 12.5% and 10.0%, respectively.
Secondly, we improved the electron extraction by inserting a crosslinked phenyl-C61-butyric acid methyl ester (PCBM) layer between TiO2 and perovskite.2 PCBM was crosslinked by 1,6-diazidohexane (DAZH) in order to overcome the solvent incompatibility issue. With such interface layers and a mixed perovskite (HC(NH2)2)0.66(CH3NH3)0.34PbI2.85Br0.15, we improved the maximum PCEs of our small area devices and modules to 18.5% and 15% (4 cm2), respectively. Moreover, by incorporating Cs+ into FA-based perovskites, we further increased the PCE of small area devices to 19.3%. This process was also be transferred to module fabrication, and perovskite modules (4 cm2) with efficiency beyond 16.4% were achieved.
W. Qiu, T. Merckx, M. Jaysankar, C. Masse de la Huerta, L. Rakocevic, W. Zhang, U. W. Paetzold, R. Gehlhaar, L. Froyen, J. Poortmans, D. Cheyns, H. J. Snaith and P. Heremans, Energy Environ. Sci., 2016, 9, 484-489.
W. Qiu, J. P. Bastos, S. Dasgupta, T. Merckx, I. Cardinaletti, M. V. C. Jenart, C. B. Nielsen, R. Gehlhaar, J. Poortmans, P. Heremans, I. McCulloch and D. Cheyns, J. Mater. Chem. A, DOI: 10.1039/c6ta08799j.
4:30 PM - ES1.4.05
Measuring Defect Tolerance and Electronic Structure in Hybrid Perovskite Solar Cell Materials
Joseph Berry 1 , K. Xerxes Steirer 1 , Philip Schulz 1 , Glenn Teeter 1 , Vladan Stevanovic 2 , Mengjin Yang 1 , Kai Zhu 1 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States, 2 , Colorado School of Mines, Golden, Colorado, United States
Photovoltaic devices based on hybrid organic-inorganic perovskite absorbers have reached outstanding performance over the past few years, surpassing power conversion efficiency of over 22%. Much of this performance has been attributed to so called “defect tolerance” in these systems that result in the predominate defects appearing within the bands. This effect should then limit the impact of defects on the functional materials properties. In this talk we present our experimental studies in which we are able to demonstrate the defect tolerance of the prototype CH3NH3PbI3 halide perovskite. By exposing the material to X-rays while performing X-ray photoemission spectroscopy we are able to induce defects while simultaneous tracking dynamicaly their impact on the material composition and electronic structure. We show our results on this protypical materials deposited on compact TiO2 and demonstrate that the valance band structure remains remarkably stable despite significant change in composition. Only after the iodine/lead ratio decreases to under 2.5 do we observe changes in the over character of the materials. We discuss the implications of these results in the context of the higher performance alloys halide perovskite materials relevant to photovoltaic applications and our inital data on some of these more complex systems.
4:45 PM - ES1.4.06
Dopable Extracting Layers as a Strategy to Stabilize Interfacial Charge Accumulation and Defect States in Perovskite Solar Cells
Vijay Venugopalan 1 2 , Francesco Lamberti 1 , Chen Tao 1 , Eva Barea 3 , Antonio Guerrero 3 , Annamaria Petrozza 1 , Juan Bisquert 3 Show Abstract
1 , Italian Inst of Technology, Milan Italy, 2 Department of Physics, Politecnico di Milano, Milan, Milan, Italy, 3 , Institute of Advanced Materials, Castellon, Castellon, Spain
Organo-Metallic Mixed Halide Perovskite (OHP’s) solar cells have received enormous attention in the last few years with efficiencies soaring beyond the 20% mark. Such rapid growth remains unprecedented in the history of photovoltaic technologies of all generations. In order to convincingly translate this progress into industries, the need of the hour is to stabilize these solar cells over long working periods. This is increasingly critical for these class of crystalline semiconductors since there is ample proof of moving ionic species in OHPs during their operation. These ionic species dissociate from the crystal lattice unit cells and move within the semiconductor thereby changing the local energetics. The energetic and trap landscapes in the bulk as well as the surfaces of the OHPs and are dynamically linked to the slow moving ions in the semiconductor. Since solar cells work with a built-in potential across the OHP, the ions accumulate at the interfaces over time. The accumulated ions prove to be an achilles heel for these devices degrading their efficiency over time.
Here, we look more closely at the surface of the OHP where these ions get accumulated. We propose a strategy to stabilize the working of the solar cells by passivating the incoming ions at the interface of a working solar cell. For this purpose, we find the comparison of a standard TiO2 interface with a passivating TiO2-PCBM interface to be an ideal starting point. We show that PCBM acts as a 'dopable' contact in the sense that it is capable of chemically reacting to the accumulated ions and getting self-doped. This self-doping effectively neutralizes the ionic buld-up at the OHP surface. We observe highly stabilized efficiencies only with such an interfacial layer which is capable of stabilizing these ions. In the absence of such a dopable extraction layer, we find a contnuous build-up of surface states and defect states that in turn cuse large electronic charge accumulations in the dark. Their absence also is the reason for the observed large capacitances of devices in dark, atypical for OHPs. We show that employing such a dopable extraction layer supresses the formation of the defect state accumulation, electronic charge accumulation and the large capacitances in these devices. Thereby we are able to obtain hysteresis free devices and high stabilized efficiencies of more than 15%. The dopable contacts also considerably increase the working stability of these cells due t a successful stabilization of the incoming ions. We hence propose that engineering interfacial layers by employing dopable semiconductors is a novel strategy to imporve the working stability of perovskite solar cells.
5:00 PM - *ES1.4.07
Charge Transport and Junction Nature of the Perovskite Solar Cell
Jiangjian Shi 1 , Dongmei Li 1 , Yanhong Luo 1 , Qingbo Meng 1 Show Abstract
1 Institute of Physics, Chinese Academy of Sciences, Beijing China
Recently, perovskite-based solar cells, has attracted worldwide interest due to their outstanding photovoltaic performance. In our lab, we focus our interest in investigating the charge transport properties and junction nature of solar cell.[1-9] Firstly, by improving the film deposition quality, an efficient single p-n heterojunction cell without the usage of an organic hole transport material layer is achieved with an efficiency of about 10.5%. [2-3] It has been found that the charge transfer properties of this type of cell can be well described by an ideal heterojunction model. The junction nature of this cell is systematically studied. The hole concentration of the perovskite absorber and junction properties can be controlled [1, 4, 5] Based on the understandings of the charge transport and junction nature of the perovskite solar cell, controlling the charge transport properties of the cell by engineering the boundary conditions has also been applied as an effective approach to enhance the cell performance. [6-8] Aside from the fast electron transport, we are also interested in the slow ion transport in this cell. By developing an in-situ modulated electrical transient method, the microscopic charge transport and recombination behind the photoelectric hysteresis have also been investigated, which demonstrates the critical role that the heterojunction electric field plays in determining the charge processes in this cell.[9, 10, 11] Deeper investigations found that the interfacial doping and defect caused by the ion migration and accumulation may be the physical origins for the wide-concerned hysteresis in this cell.
J. J. Shi, Q.-B. Meng et al, Small, 2015, 11, 2472.
J. Shi, J. Dong, Q. B. Meng, et al., Appl. Phys. Lett. 2014, 104, 063901.
J. Shi, Y. Luo, Q. Meng et al, ACS Appl. Mater. Interfaces 2014, 6, 9711.
J.-J. Shi, Q.-B. Meng et al, Chemphyschem 2015, 16, 842.
J. Dong, Qingbo Meng et al, Chem. Commun., 2014, 50, 13381.
J. Dong, J. Shi, Q. Meng, et al, Applied Physics Letters 2015, 107 (7), 073507.
J. Shi, Q. B. Meng, Q. Chen, Chin. Phys. Lett., 2013, 30, 128402.
H. Wei, J. Shi, Q. Meng et al, Phys. Chem. Chem. Phys. 2015, 17 (7), 4937-4944.
J. Shi, D. Li, Q. B. Meng, et al., Rev. Sci. Instrum. Revised.
J. Shi, X. Xu, Q. B. Meng, et al, Appl. Phys. Lett. 107, 163901, 2015.
J. Shi, H. Zhang, Q. B. Meng, et al., Small 12, 5288 (2016).
5:30 PM - ES1.4.08
Impact of the Interface Charge-Injection on CH3NH3PbI3 Perovskite Solar Cell Performance Investigated by Time-Resolved Photoluminescence and Photocurrent Measurements
Taketo Handa 1 , David Tex 1 , Ai Shimazaki 1 , Atsushi Wakamiya 1 , Yoshihiko Kanemitsu 1 Show Abstract
1 , Kyoto University, Uji Japan
Organic-inorganic halide perovskite solar cells have received much attention from the photovoltaic community because of their high conversion efficiencies exceeding 20%. So far, comprehensive studies on the perovskite thin films and single crystals have revealed their intrinsic superior optoelectronic properties . For further improvement of the conversion efficiency, the carrier dynamics in actual devices have to be clarified to understand how the optimum device architecture should look like . In particular, carrier-injection from the perovskite absorber layer into the carrier transport layer is important for the device performance. Photoluminescence (PL) techniques are usually employed to investigate injection properties. However, PL is also additionally affected by traps and defects within the perovskite layer and also at the heterointerface. On the other hand, photocurrent (PC) directly reflects the net charge-carrier flow through the whole device, and therefore a combination of PL and PC enables us to investigate the details of the carrier-injection.
In this study, we measured the excitation fluence dependence of time-resolved PL and PC for CH3NH3PbI3 solar cells, and evaluated carrier-injection mechanism at the interface. We prepared a solar cell device consisting of FTO/compact TiO2/mesoporous TiO2/CH3NH3PbI3/Spiro-OMeTAD/Au, with a conversion efficiency of ~17%. For the excitation of the perovskite layer, a pulsed picosecond laser with wavelength of 650nm was used. We found that the PL lifetime of the sample becomes longer with increasing excitation intensity, which is completely different from the trend observed for thin film samples. This peculiar trend indicates that carrier-injection becomes slower under high excitation, i.e., a significant decrease of the carrier-injection efficiency occurs above 100 nJ cm-2. Simultaneous PL and PC measurements revealed that the external quantum efficiency (EQE) maintains a constant value of 80% below excitation intensities of 100 nJ cm-2, but drops above. These results indicate that the injection at the heterointerface limits the photovoltaic performance of the device. In addition, by solving a simple rate equation system, we discuss how the carrier-injection, nonradiative, and radiative recombination affect the performance of perovskite solar cells.
This work was supported by CREST, JST.
 Y. Yamada et al., J. Am. Chem. Soc. 136, 11610 (2014); Y. Yamada et al., J. Am. Chem. Soc.137, 10456 (2015); L. M. Pazos-Outon et al., Science 351, 1430 (2016).
 T. Handa et al., Opt. Express. 24, A917 (2016); D. Yamashita et al., J. Phys, Chem. Lett. 7, 3186 (2016).
5:45 PM - ES1.4.09
Computaional I-V Curve of Perovskite Solar Cell with Surface Boundary Induced Capacitance
Satoshi Uchida 1 , Ludmila Cojocaru 2 , Piyankarage V. V. Jayaweera 3 , Shoji Kaneko 3 , Jotaro Nakazaki 2 , Takaya Kubo 2 , Hiroshi Segawa 2 Show Abstract
1 Komaba Organization for Educational Excellence College of Arts and Sciences, The University of Tokyo, Tokyo Japan, 2 Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo Japan, 3 , SPD Laboratory, Inc., Hamamatsu Japan
We investigated the origin of hysteresis in I-V curves of a planar perovskite cell using different equivalent circuit models. A planar cells showing huge hysteresis with PCE 18.0% on reverse scan and 8.8% on forward scan was used for validating the equivalent circuits. We found that the conventional equivalent circuit with a diode, a series resistance and a shunt resistance does not reproduce the hysteresis of I-V curves. Even for the incorporation of a capacitive component in the circuit, the model also did not match the experimental I-V curves.
However, an equivalent circuit model composed of two series connected diodes, two capacitors, two shunt resistances and a series resistance clearly reproduced the hysteretic I-V curves. For this model, fitting parameters (Rs, Rsh1, Rsh2,) were chosen by using calculated series and shunt resistance values from experimental I-V data. Initial C1 and C2 were randomly selected. Then parameters were optimized (by trial and error method) to minimize deviation between simulated and experimental curves. According to this equivalent circuit model, the computationally simulated curves matched closely with the experimental one. This suggests that perovskite cell has two active interfaces; TiO2/CH3NH3PbI3 and CH3NH3PbI3/spiro-OMeTAD. Hysteresis is essentially caused by carrier accumulation at these active interfaces. The electrical capacitances generated by defects due to the lattice mismatch at the TiO2/CH3NH3PbI3 and CH3NH3PbI3/spiro-OMeTAD interface are truly responsible for the hysteresis in the perovskite solar cells.
Based on above experience and knowledge, we also examined to evaluate the cell performance at low light intensity condition. Very surprisingly, due to the charge / discharge property with internal capacitance, we found the limitation to define the cell performance from the I-V curve because of the fake current. To solve this issue, we newly propose the Maximum Power Point Tracking (MPPT) technique to define the most accurate cell performance of the hysteric device.
ES1.5: Poster Session I
Wednesday AM, April 19, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ES1.5.01
Photonic Curing of Inkjet Printed TiO2 Films for Perovskite Solar Cells
Briley Bourgeois 1 , Brian Riggs 1 , Shiva Adireddy 1 , Sijun Luo 1 , Douglas Chrisey 1 , Matt Escarra 1 Show Abstract
1 , Tulane University, New Orleans, Louisiana, United States
Much of the research on perovskite photovoltaics has been centered on continued improvement of the overall device efficiency and addressing stability concerns of the perovskite material, while relatively little effort has been devoted towards the implementation of scalable manufacturing techniques for the synthesis of such devices. A major obstacle in the scalability of these devices lies in the TiO2 layer used in most device architectures. Currently, TiO2 deposition utilizes high temperature, time consuming, batch-to-batch processing that requires rigid, high-cost substrates. Inkjet printing and high intensity photonic curing are roll-to-roll processing methods that can replace traditional methods for fabricating TiO2 films for perovskite photovoltaics.
Photoactive metal organic precursors and high intensity photonic radiation are used to rapidly synthesize TiO2 films through non-equilibrium heating and photodecomposition, allowing the use of low temperature polymer substrates. The photonic curing process forms TiO2 films in at least 1/60th the time needed for traditional processing methods. With a material utilization of 95% (as opposed to 5% for spin-coating), inkjet printing is an efficient roll-to-roll processing technique that also allows for the creation of customizable device patterns.
Raman spectroscopy has been utilized to examine the phase of the resulting TiO2 and has revealed an inherent graphitic carbon composite. Controlling the precursor concentration in the inks from 3.5% to 20% by weight allows for control over phase between anatase and amorphous TiO2 as well as control over film thickness from 20 to 200 nanometers. By adding complementary photoactive chemicals to the standard inks, crystallinity could be improved and rutile TiO2 could be formed. Optical profilometry and scanning electron microscopy have been used to examine the film thickness and morphology. Film thickness is mainly controlled through precursor concentration while pulse fluence shows control over morphology and phase. Varying the fluence from 4.5 to 8.5 J/cm2 changed the morphology from uniform, smooth films to mesoporous structured films. Electrical conductivity measurements are being used to examine the electrical properties of these low temperature films and show conductivities comparable to thermally annealed films. Optical analysis is being used to examine properties such as index and absorption. Our ongoing work includes synthesis of the other key perovskite photovoltaic layers and full perovskite solar cell devices.
9:00 PM - ES1.5.02
Towards Flexible NiOx-Based Perovskite Solar Cells
Xingtian Yin 1 , Wenxiu Que 1 Show Abstract
1 , Xi'an Jiaotong University, Xi'an, Shaanxi, China
Organic-inorganic perovskite materials are very suitable for flexible devices because high quality perovskite films can be deposited through a low temperature solution process. However, the power conversion efficiency (PCE) of flexible perovskite solar cells is still much lower than that of rigid devices partially due to the poor carrier transport properties of contact films employed in flexible devices. Besides, the frequently used organic hole transport materials such as PEDOT:PSS and Spiro-OMTAD also brought stability problems to the devices. In this presentation, we will introduce several methods to prepare high quality NiOx hole transport films for perovskite solar cells, and the focus will be put on some low temperature derived NiOx films which is very suitable for flexible devices. Particularly, we demonstrated a solution-derived NiOx-based inverted planar heterojunction perovskite solar cell with a PCE of as high as 16.47% on an ITO-glass substrate. The NiOx film was deposited at a temperature of 130 oC without any post treatment. Detailed study on the interfacial carriers transfer and charge recombination processes proved it to be an efficient hole contact for perovskite film. Particularly, the low temperature deposition process made it very suitable and attractive for flexible devices. A preliminary PCE of 13.43% was demonstrated with NiOx-based flexible perovskite solar cell using an ITO-PEN (polyethylene naphthalate) substrate. Besides, a solvothermal method was also employed to prepare ultrafine crystalline NiOx nanoparticles, which can be well dispersed in ethanol and stable for weeks. High quality NiOx films were able to be deposited onto flexible substrates from such kind of NiOx colloids, based on which efficient flexible perovskite solar cells can also be achieved..
9:00 PM - ES1.5.03
Large Size Planar Perovskite Solar Cells Produced from Porous PbI2(NMP) Complexes
Yimhyun Jo 1 , Dong Suk Kim 1 Show Abstract
1 , Korea Institute of Energy Research, Ulsan Korea (the Republic of)
Solution processed perovskite solar cells are recently attracted with big interest because of their high performance and low-cost process. However, realization of the devices for practical filed is hindered by troubles in fabrication of large scale devices with high performance. Here, it is introduced a simple method for preparation of porous PbI2(NMP) complex to obtain smooth, crystalline and extremely uniform hybrid perovskite film over large area around 100 cm2. This method enables us to realize the large scale hybrid perovskite solar cells with high performance for commercialization.
9:00 PM - ES1.5.04
Controlling Perovskite Crystal Growth by Thermal Gradient
Karsten Bruening 2 1 , Michael Toney 2 , Christopher Tassone 2 Show Abstract
2 SSRL, SLAC National Accelerator Laboratory, Menlo Park, California, United States, 1 , Stanford University, Stanford, California, United States
It is well established that perovskite single crystals have superior opto-electronic properties to thin films (e.g. carrier lifetime). It is thus desirable to understand and control the crystal growth in order to optimize the grain morphology of thin films to improve the power conversion efficiency, while maintaining the ease of solution processability for large scale fabrication.
We introduce a flash annealing procedure with a temperature gradient which allows us to efficiently grow large grains (>2µm) in a few seconds from a precursor solution consisting of PbCl2 and MAI. We followed the crystallization kinetics in situ using X-ray diffraction with a time resolution of 100ms and we identified distinct regimes of highly oriented crystallite growth. In the initial stage of crystallization, the (100) planes of the cubic lattice orient normal to the substrate, while in later stages the misorientation increases, even though the monolithic grains appear to stretch across the entire thickness of the film as seen in cross-sectional SEM. Thus, the growth mechanism and final morphology are vastly different from conventional hot plate annealing.
Besides gaining insight into the fundamentals of the crystallization mechanism, this particular method of flash annealing might be attractive to upscaling, as it is able to robustly grow large grain films on time scales of a few seconds.
9:00 PM - ES1.5.05
New Concepts in Reinforced, Segmented Perovskite Solar Cell Design with Polymer Scaffolding
Adam Printz 1 , Nicholas Rolston 1 , Brian Watson 1 , Reinhold Dauskardt 1 Show Abstract
1 , Stanford University, Stanford, California, United States
Perovskite solar cells are promising photovoltaic technologies due to their high efficiency, insensitivity to defects and low fabrication cost, but viability of the technology requires significant improvements in thermomechanical reliability. To address the challenge of perovskite mechanical instability, a new concept in perovskite device architecture is reported—a reinforcing, patterned scaffold in which uniform and efficient perovskite devices are created. The architecture of the scaffold allows for the device to be partitioned into thousands of smaller cells, each of which is mechanically isolated and shielded. The perovskite-infused scaffolds exhibited a fracture resistance of ~13 ± 3 J m–2—a 30-fold increase over previously reported planar perovskite devices while still maintaining efficiencies comparable to the planar devices (11.7 ± 0.2% versus 14.5 ± 1.7% for methylammonium lead iodide perovskite devices). Notably, the efficiencies of perovskite-infused scaffold devices were found to be predictable by a simple geometric model, and the individual cells maintained the same efficiency and fill factors as the planar device. Design parameters for the scaffold architecture, including the role of wall widths and height, and cell size, shape, and periodicity will be discussed. These parameters allow for significant tunability of the device performance and thermomechanical behavior. This development is a significant step toward demonstrating robust perovskite solar cells with major improvements in reliability and service lifetimes that can ultimately compete with CIGS, CdTe, and c-Si cells.
9:00 PM - ES1.5.06
High Efficient Flexible Perovskite Solar Cells Based on Indium-Free Solution-Processed Silver Nanowire Composite Transparent Electrode
Eunsong Lee 1 , Hyeok-Chan Kwon 1 , Jihoon Ahn 1 , Hongseuk Lee 1 , Hyewon Hwang 1 , Sunihl Ma 1 , Jooho Moon 1 Show Abstract
1 Materials Science and Engineering, Yonsei University, Seoul Korea (the Republic of)
For transparent electrode as a bottom electrode in perovskite solar cells, either indium tin oxide (ITO) or fluorine-doped tin oxide (FTO) is most widely utilized. However, indium is rare metal which is improper to mass production and commercialization. Moreover, conventional method for ITO or FTO electrode resorts to vacuum based deposition, which results in cost rise and complexity. ITO electrode could be fabricated by solution process, but the solution derived ITO exhibits high resistance, which makes it difficult to be applied in the practical device application. Furthermore, brittleness of ITO makes it difficult to apply on flexible substrates. Herein, we introduce the solution-processed transparent composite electrode consists of silver nanowires and indium-free metal oxides. Although there are several studies on silver nanowire based bottom electrodes for perovskite solar cells, they relied on vacuum processed ITO. As a metal oxide layer above silver nanowire, we adopt amorphous aluminum-doped zinc oxide (AZO). These multi-layered composite electrodes need to i) be annealed at low temperature because silver nanowire could be damaged at above 200oC and ii) be protected from diffusion of halogen ions into the perovskite precursor, which leads to the degradation of silver nanowire, and iii) maintain high conductivity as well as transmittance. By optimizing the density of silver nanowire and the thickness of upper AZO layer, we were able to protect the silver nanowires from the halogen ions diffusion during the fabrication of perovskite solar cells. As a result, we could obtain nearly 12% of power conversion efficiency on both rigid and flexible substrates. About 90% of initial efficiency was remained after 200 bending cycles due to highly stretchable properties of silver nanowire based composite, while PCE of ITO electrode based cell was decreased due to cracks on ITO formed during bending. Our successful application of indium-free solution processable electrode on flexible perovskite solar cell suggests the possibility of roll-to-roll mass production.
9:00 PM - ES1.5.07
Extent of Methylammonium Lead Iodide Hydration by Atmosphere in Full Devices
Genevieve Hall 1 , Michael Stuckelberger 1 , Bradley West 1 , Jessi Hartman 2 , Ji-Sang Park 3 , Jeremie Werner 4 , Bjoern Niesen 4 , Christophe Ballif 4 , Maria Chan 3 , David Fenning 5 , Mariana Bertoni 1 Show Abstract
1 , Arizona State University, Tempe, Arizona, United States, 2 , UC Davis, Davis, California, United States, 3 , Argonne National Laboratory, Lemont, Illinois, United States, 4 , Ecole Polytechnique Federale de Lausanne, Neuchatel Switzerland, 5 , UC San Diego, San Diego, California, United States
The low production costs, abundant precursors, and high efficiencies of perovskite solar cells (PSCs) poise them to disrupt the photovoltaics market. However, the archetypal absorber material, methylammonium lead iodide (MAPI), rapidly degrades upon exposure to atmosphere. Understanding its degradation mechanism may enable rational material and device design to extend the service lifetime of PSCs.
Water vapor, in particular, contributes to the degradation of MAPI, but the full process is not well understood. Water vapor reversibly hydrates MAPI to a monohydrate (CH3NH3PbI3 . H2O) and then irreversibly to a dihydrate (CH3NH3PbI3 . 2H2O) . Further hydration irreversibly degrades MAPI to solid lead iodide and gaseous methylammonium and hydrogen iodide. The monohydrate is stable at 77% relative humidity and the absorption of water into anhydrous MAPI is exergonic . Therefore, it is likely that MAPI is hydrated to lower degrees at humidity levels below 77%, which is relevant for devices. In our first principles density functional theory (DFT) calculations, we find that intercalated water is associated with changes in the volume, and therefore band gap.
In this work, we present the effect of hydration on the band gap of MAPI in operationally relevant humidity ranges. We studied the effect of atmospheric composition, pressure, and temperature on the band gap and open circuit voltage of state-of-the-art MAPI-based devices . Photoluminescence and open-circuit voltage measurements show a partially reversible, water-induced band gap increase. An analysis of the thermodynamics of water intercalation free energy, as calculated from DFT, as a function of pressure indicates the probability of water release during the pressures assessed in the experiment. This supports the idea that partial hydration and dehydration of MAPI occurs in full devices, despite the barriers of charge transport layers and electrodes. We expect these band gap changes to be mirrored in variations of the open-circuit voltage. Results on single crystal samples and a variety of cell structures will be presented.
1. Leguy et al. Chem. Mater. 2015 27, 3397.
2. Zhang et al. J. Phys. Chem. C 2015 119, 22370.
3. Werner et al. Solar Energy Materials and Solar Cells 2015, 141, 407.
9:00 PM - ES1.5.08
Modeling the Growth Mechanism and Morphology of Solution-Processed Monolayers on Perovskite Surfaces for Solar Cell Applications
Mohammad Fuad Nur Taufique 1 , SM Mortuza 1 , Aniruddha Dive 1 , Soumik Banerjee 1 Show Abstract
1 , Washington State University, Pullman, Washington, United States
Solution-processed planar perovskite solar cells (PSCs) have seen tremendous improvement in efficiency over the past few years and have achieved power conversion efficiencies of greater than 20%. However, planar PSCs are prone to hysteresis and current instabilities. Recent studies suggest that employing electron transport layers (ETLs) comprising fullerene derivatives, such as [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) on top of perovskite crystal faces can reduce hysteresis by passivating deep trap states. Therefore, it is important to study the morphology of PCBM layers formed on top of perovskite during solution-processing in order to fabricate a compact ETL with fewer defects. With that objective, we developed and employed a multiscale model based on molecular dynamics (MD) and kinetic Monte Carlo (kMC) method to establish a relationship between deposition rate and surface coverage of PCBMs on perovskite surface.
At first, we performed MD simulation of PCBMs solvated in chlorobenzene near (110) and (100) perovskite surfaces to gain physical insight into mechanism for growth of PCBM on perovskite surfaces. Results from MD simulation suggested strong orientational preferences between PCBM and the perovskite surface during deposition of ETL. In particular, the carbonyl oxygen atom of PCBM showed strong attachment with the terminating Pb and H atoms in (110) and (100) perovskite surfaces respectively, driven by strong electrostatic interactions. On the other hand, the phenyl moiety showed weak association with (100) perovskite surface thus enabling two prolonged docking that might help with efficient charge transfer. In-plane ordering of deposited PBCMs on perovskite surfaces suggested that a more densely packed monolayer was formed on the (110) surface compare to that on the (100) surface and might lead to more efficient charge transport from ETL to electrode.
In order to determine surface coverage of perovskite by deposited PCBMs at much larger time and length scales, we performed kMC calculations of surface deposition based on calculated rates of distinct deposition events from MD simulations. The kMC simulations established that the PCBM monolayer deposited from less concentrated PCBM stock solution comprises uniformly distributed clusters and hence creates uniform films with fewer defects compared to that deposited from a more concentrated PCBM stock solution. Additionally, results from kMC simulations suggest that the PCBM deposition rate was significantly greater at the early stages of deposition and decreased with time due to steric hindrance and fewer available spaces for deposition on the perovskite surface. We believe that the multiscale model can open a new frontier for designing compacted ETLs for planar PSCs by determining optimum solution processing parameters.
9:00 PM - ES1.5.09
A Pure and Stable Intermediate Phase is Key to Growing Aligned and Vertically Monolithic Perovskite Crystals for Efficient PIN Planar Perovskite Solar Cells with High Processibility and Stability
Yang Bai 1 Show Abstract
1 , Hong Kong University of Science and Technology, Hong Kong Hong Kong
Solvent engineering has been extensively used to control and grow the high-quality perovskite layer for solar cells by forming intermediate phases. However, the intermediate phase formation is often poorly understood and its effects on the perovskite layer growth are still elusive. Here, we have conducted a systematic and in-depth study on the above two issues through a strict control over the DMSO/DMF ratio in CH3NH3PbI3 perovskite solutions, and thus an effective control over the compositions of intermediate films. The films thus obtained, including perovskite, perovskite/MA2Pb3I8(DMSO)2 and MA2Pb3I8(DMSO)2, afford perovskite crystals via down-growth, down-and up-growth, and up-growth mechanisms, respectively. Significantly, the up-growth perovskite crystals from the pure MA2Pb3I8(DMSO)2 exhibits the best interface contact with NiO substrate, optimal alignment without horizontal grain boundaries, and a relatively large grain size, which facilitate charge transfer and reduce charge recombination in PSCs. As a result, the PIN planar PSCs based on NiO have achieved a PCE of 18.4%, a value which is among the highest for NiO-based PSCs, with the highest stability among the tested sample cells. Furthermore, the pure MA2Pb3I8(DMSO)2 intermediate phase presents a high long-term stability, which enlarges the operating window for perovskite deposition and thus considerably improves the device processibility.
9:00 PM - ES1.5.10
Unveiling a Key Intermediate in Solvent Vapor Post-Annealing to Enlarge Crystalline Domains of Organometal Halide Perovskite Films
Shuang Xiao 1 Show Abstract
1 , The Hong Kong University of Science and Technology, Hong Kong China
Hybrid organic/inorganic perovskite solar cells (PSCs) have shown great potential in meeting the future challenges in energy and environment. Solvent vapor-assisted post treatment strategies were developed to improve the perovskite film quality for achieving higher efficiency. However, the intrinsic working mechanisms of these strategies have not been well understood yet. In the present work, we have identified a MA2Pb3I8(DMSO)2 intermediate phase formed during the annealing process of MAPbI3 in DMSO atmosphere and located the reaction sites at perovskite grain boundaries by observing and rationalizing the growth of nanorods of the intermediate. This enabled us to propose and validate an intermediate assisted grain-coarsening model, which highlights the activation energy reduction for grain boundary migration. Leveraging this mechanism, we used MABr/DMSO mixed vapor to further enhance grain boundary migration kinetics and successfully obtained even larger grains, leading to an impressive improvement in power conversion efficiency (17.64%) relative to the pristine PSCs (15.13%). The revelation of grain boundary migration assisted grain growth provides a guide for the future development of polycrystalline perovskite thin film solar cells.
9:00 PM - ES1.5.12
Triple-Cation Mixed-Halide Perovskites—Fabrication of Efficient, Annealing-Free, Air-Stable Solar Cells Enabled by Pb(SCN)2 Additive
Yong Sun 1 , Jiajun Peng 1 , Yani Chen 1 , Yingshan Yao 1 , Ziqi Liang 1 Show Abstract
1 , Fudan University, Shanghai China
Organo-metal halide perovskites have suffered undesirably from structural and thermal instabilities. Moreover, thermal annealing is often indispensable to the crystallization of perovskites and removal of residual solvents, which is unsuitable for scalable fabrication of flexible solar modules. Herein, we demonstrate the non-thermal annealing fabrication of a novel type of air-stable triple-cation mixed-halide perovskites, FA0.7MA0.2Cs0.1Pb(I5/6Br1/6)3 (FMC) by incorporation of Pb(SCN)2 additive. It is found that adding Pb(SCN)2 functions the same as thermal annealing process by not only improving the crystallinity and optical absorption of perovskites, but also hindering the formation of morphological defects and non-radiative recombination. Furthermore, such Pb(SCN)2-treated FMC unannealed films present micrometer-sized crystal grains and remarkably high moisture stability. Planar solar cells built upon these unannealed films exhibit a high PCE of ~14% with significantly suppressed hysteresis phenomenon compared to those of thermal annealing. The corresponding room-temperature fabricated flexible solar cell shows an impressive PCE of ~11%. This work offers a new avenue to low-temperature fabrication of air-stable, flexible and high-efficiency perovskite solar cells.
9:00 PM - ES1.5.13
Soft-Cover Deposition of Scaling-Up Uniform Perovskite Thin Films for High Cost-Performance Solar Cells
Chen Han 1 , Fei Ye 1 , Xudong Yang 1 , Liyuan Han 1 2 Show Abstract
1 , Shanghai Jiaotong University, Shanghai China, 2 , National Institute for Materials Science, Tsukuba Japan
Low-cost and high energy conversion efficiency are the crucial factors for large scale application of solar cells. In recent years, a promising high cost-performance photovoltaic technology, organometal halide perovskite solar cells (PSCs), has attracted great attention. However, most of the reported high efficiencies were obtained on small working area of about 0.1 cm2 with the material utilization ratio of only 1% during the film deposition, which actually hinders the advance of future application of PSCs. Here we present soft-cover deposition (SCD) method where the surface wettability, solution viscosity and thermal crystallization are the processing key factors, for the deposition of uniform perovskite films with high material utilization ratio. Scaling-up, pinhole-free, large crystal grain and rough-border-free perovskite films were obtained over a large area of 51 cm2, which was processed continuously in ambient air with a significantly enhancement in material utilization ratio up to ~80%. Highly reproducible power conversion efficiencies up to 17.6% were achieved on unit cells with working area of 1 cm2, leading to a high overall cost-performance. We believe that the present SCD technology will benefit the low-cost fabrication of highly efficient perovskite solar cells and open a route for the deposition of other solution processed thin-films.
9:00 PM - ES1.5.15
Loading Dependent Electrical Properties of Novel Hybrid Perovskite/Polymer Composite
John Murphy 1 3 , Jessica Andriolo 2 3 , Jack Skinner 4 3 Show Abstract
1 Materials Science, Montana Tech of the University of Montana, Butte, Montana, United States, 3 , Montana Tech Nanotechnology Laboratory, Butte, Montana, United States, 2 Bioengineering, Montana Tech of the University of Montana, Butte, Montana, United States, 4 General Engineering, Montana Tech of the University of Montana, Butte, Montana, United States
Hybrid organic-inorganic perovskites (HOIPs) have been established as a material to supplement and potentially replace silicon in low cost solar cells. HOIP solar cells are attractive commercially for several reasons: low precursor materials costs, high defect tolerance, and low processing costs. However, HOIPs are inherently instable and are particularly susceptible to moisture-driven degradation. As a consequence of these instabilities HOIP solar cell device lifetimes are not sufficiently long for manufacturing cost payback. Chemical instabilities must be addressed in order for successful large scale implementation of HOIPs in an economically attractive solar cell.
A solventless synthesis method which utilizes a polymer melt in order to thermodynamically drive the HOIP precursors to react in the absence of a coordinating solvent has been previously demonstrated. Synthesis within polymer melt results in a composite material in which, HOIP microcrystallites exist in a protective polymer matrix with an improved resistance to moisture-driven degradation. Additionally, the polymer melt synthesis technique has been used in tandem with a scalable melt electrospinning process to produce composite microfibers. Polymer/HOIP composite materials have demonstrated improved moisture stability, but other properties conducive to device fabrication, such as conductivity, have not yet been studied. The electrical behavior of the polymer/HOIP composite and the relationship it has to the loading of the composite must be well understood for successful integration into a useful solar cell.
This research will focus on the effect that various HOIP loadings have on the electrical properties of the novel composite microfibers, as well as bulk composite samples. Furthermore, the microstructure of the composite will be actively controlled for higher reproducibility between samples. Active control will be facilitated by preprocessing the inorganic perovskite precursor using a simple solvent/anti-solvent precipitation step to control inorganic crystallite size. The electrical properties of the composite material will be investigated using a source meter to generate current-voltage plots to determine necessary loading of HOIPs to elicit conductivity in the composite material. X-ray diffraction (XRD) will be utilized to confirm the presence of tetragonal phase of CH3NH3PbI3 perovskite and assess the relative amount of unreacted PbI2 present in the composite material after synthesis. Scanning electron microscopy (SEM) paired with energy dispersive spectroscopy (EDS) will allow the microstructure of the composite material to be determined. Data collected via XRD and SEM-EDS will allow parametric analysis of the loading dependent properties of the composite material. Understanding the relationship between loading and electrical properties of the composite material will provide a path towards integration into a solar cell with improved stability and improved device lifetime.
9:00 PM - ES1.5.16
Fabrication of Formamidinium Lead Bromide Perovskite Solar Cells Yielding High Open-Circuit Voltage Using New Hole-Transporting Materials
Neha Arora 1 , Mohammad Ibrahim Dar 1 , Shaik Mohammed Zakeeruddin 1 , Michael Graetzel 1 Show Abstract
1 Laboratory of Photonics and Interfaces, Ecole Polytechnique Federale de Lausanne, Lausanne Switzerland
A new and simple hole-transporting material (HTM) has been synthesized and employed successfully in the fabrication of formamidinium lead bromide perovskite solar cells yielding high open-circuit voltage (VOC). The systematic characterization of the new hole-transporting material was carried out through cyclic voltammetry and ultraviolet-visible and photoluminescence spectroscopy. While retaining the mesoporous TiO2 based architecture, the fabrication of FAPbBr3 devices yielding an impressive photovoltage of above 1.5 V and a power conversion efficiency of 8% was realized. Spectro-electrochemical measurements revealed a higher oxidation potential for new hole-transporting material, which rationalizes the higher VOC obtained. A combination of techniques including transient spectroscopy, time-integrated and time- resolved photoluminescence were employed to further investigate the various photophysical processes occurring within the perovskite films and across various interfaces. The current−voltage curves exhibited negligible hysteresis, and the photoconversion efficiency showed good reproducibility. Also, it is noteworthy that the devices based on the new HTM demonstrated stable photovoltaic performance for more than 100 h under 1 sun illumination at maximum power point tracking. In addition to the studies revealing the role of the perovskite light harvester and HTM in determining the VOC, results of stability measurements will be presented.
9:00 PM - ES1.5.17
Degradation of MAPbI3—What We Know/What We Don’t Know
Angus Kingon 1 , Onkar Game 1 , Nitin Padture 1 , Seunghyun Kim 1 Show Abstract
1 , Brown University, Providence, Rhode Island, United States
There is currently a great deal of justified excitement about the hybrid perovskite (ABX3) based solar cells. An understanding of the degradation of the photovoltaic material MAPbI3 under controlled conditions is an essential prerequisite for successful commercialization, and for attaining the required operating lifetimes (>25 years for grid utility products). However, well-designed experimental studies of degradation processes are currently limited, resulting in little understanding of the competitive degradation processes that may ultimately impact service lifetimes. This presentation describes investigations into three basic processes that are likely to ultimately play defining roles within lifetime-determining degradation mechanisms. The three are: moisture exposure effects; confinement and gas overpressure effects; and the role of mobile ions.
In our study we show that moisture can play the roles of both essential ingredient and bad actor. We show that some moisture and environmental exposure improves the transport characteristics of MAPbI3 test capacitor structures, in comparison with controls. At higher moisture concentrations and exposures, reaction with MAPbI3 is strongly deleterious, and these reactions are described. We show that the reaction rates are a function of the engineered microstructures.
A second mechanism contributing to the degradation is the loss of volatile components of the MAPbI3, specifically volatilization of MAI. Volatilization conditions are described, including the concentrations of vacancies that can be tolerated in the single phase material. We show that this decomposition is strongly dependent on gas overpressures and confinement. Our studies bear directly on encapsulation procedures for commercial products.
The ion vacancy concentrations which result from MAI volatilization impact the mobilities of the ion vacancies. We have recently described the conditions under which iodide vacancies and A-site vacancies are mobile, and we quantified their relative mobilities. The impact of vacancy migration on electronic transport is described, and more importantly we speculate on the impact on the long term operation of photovoltaic devices.
We conclude with comments on the relative importance of these degradation mechanisms, and discuss strategies for ensuring the required service lifetimes for PV products.
9:00 PM - ES1.5.18
Environmental-Friendly Design of Perovskite Solar Cells—Cooperation between Environmental and Materials Sciences
Steffi Weyand 2 , Carolin Wittich 1 , Liselotte Schebek 2 Show Abstract
2 Institute IWAR, material flow analysis and resource economy, Technische Universität Darmstadt, Darmstadt, Hessen, Germany, 1 , Technische Universität Darmstadt, Darmstadt Germany
Climate mitigation strategies are one of the most important tasks of the energy sector. The transition from a traditional, fossil based to a sustainable and reliable energy supply system is only achievable with the innovation of new energy technologies. The requirements of innovation are not only the design and development of new technologies but also the advancement of competitive, dependable and environmental friendly solutions for the energy system in general. To compare the environmental performance of new energy technologies with existing ones, sustainability methods, e.g. the Life Cycle Assessment (LCA), can be employed to analyse the environmental impacts over the whole life cycle of new technologies.
In this work, the perovskite solar cells as one of those innovations of the photovoltaic sector are reviewed and their development is accompanied from an environmental point of view. Concerning this, we started with a systematic literature review on LCA studies of perovskites. There are just four studies which analyse different environmental impacts categories such as climate change or toxicity during the whole life cycle of perovskites on a laboratory scale and one study which analyses an up-scaled perovskite solar cell on a fabricated large scale level. The results of these LCA studies differ significantly and the differences are not always comprehensible to material scientists. For this reason, we compare the LCA results of these studies and explain the origin of these differences to non-LCA-experts.
In the next step, we conducted an own LCA study in cooperation with perovskite researchers to include the environmental perspective in the development processes as well as to get some insights of the environmental benefits and drawbacks of perovskites. This study was complemented with a sensitivity analysis, to investigate the effects of parameters like lifetime or efficiencies. The study shows the environmental performance of the state of the art as well as the environmental potentials of perovskites for a further development and improvement of the design.
All in all, the cooperation possibilities between environmental and material sciences are presented and the resulting benefits regarding environmental-friendly design are illustrated.
9:00 PM - ES1.5.19
Optical Annealing for Improved Photostability of Mixed Halide Perovskites
Wenhao Li 1 , Rashid Zia 1 Show Abstract
1 , Brown University, Providence, Rhode Island, United States
The tunable bandgaps of mixed halide organic-inorganic perovskites make them promising candidates for a range of optoelectronic device applications, including tandem solar cells. However, it has been well documented that mixed halide systems, such as MAPbI(3-x)Br(x), segregate under illumination at solar relevant powers. The origins of this phase segregation have been widely discussed, and several mechanisms have been proposed based on thermodynamic instabilities and light-induced electric field effects. However, the reported stabilities for mixed-halide thin films are well below those of single crystal samples. This suggests that light-induced segregation may be a surface and defect driven process, rather than an intrinsic property of the bulk material.
In this presentation, we will show how optical annealing can be used to improve the photostability of mixed-halide perovskite thin films. Specifically, we will present experimental results that show how controlled illumination of MAPbI(3-x)Br(x) inhibits subsequent phase segregation at solar relevant powers for periods of several days. We will also present parametric studies highlighting the inhomogeneity of photostability within thin-film samples, and will discuss the implications of these studies for mitigating phase-segregation in device applications.
9:00 PM - ES1.5.20
A New Criteria Helping in Finding Novel Stable Hybrid Halide Perovskites
Chao Zheng 1 , Oleg Rubel 1 Show Abstract
1 , McMaster University, Hamilton, Ontario, Canada
The efficiencies of hybrid organic-inorganic perovskite solar cells have already roared up to over 20%. The main obstacle hindering the commercialization of hybrid organic perovskite solar cells is the instability of the active material. Despite the success of first-principle calculations in predicting stability of perovskite structures, the origin of instability and avenues for its improvement remain unclear. We proposed a new mechanism of this instability and set an extra criteria to filtrate new stable hybrid halide perovskites aimed for photovoltaics.
We extend the Born-Haber cycle to analysis of energy components of the reaction enthalpies for various perovskite structures using the density functional theory (DFT). The formation process of CH3NH3PbI3 from solid CH3NH3I and PbI2 compounds can be subdivided into several consecutive steps. The initial step—molecularization—involves breaking the CH3NH3I and PbI2 lattice structures and formation of CH3NH3 and PbI3 molecules. The next step is the ionization of CH3NH3 molecule followed by the ionization of PbI3. Finally, electrically charged CH3NH3+ and PbI3− complex ions are combined to form CH3NH3PbI3 crystalline structure. The amount of energy ΔHlatt released in this reaction is called the lattice energy of the hybrid organic perovskite structure. This concludes the Born-Haber cycle of CH3NH3PbI3. The total reaction enthalpy is compiled from enthalpies of individual steps of the cycle.
The analysis of various contributions to the reaction enthalpies of hybrid halide perovskites shows that the molecularization and lattice energies largely cancel each other. The ionization energy is the remaining contribution to the reaction enthalpy that ultimately controls the balance of the reaction. The lower ΔHion is, the more stable the compound.
Among the variety of organic cations CN3H6+ has the ionization energies lower than that for CH3NH3+ cation making it a favourable candidate for perovskites with improved stability. However, the size of CN3H6 molecules is greater than CH3NH3, which raises the tolerance factor above the upper formability limit of 0.95. A large size of the organic molecule hinders formability of CN3H6PbI3 perovksite structure.
In order to achieve a chemically stable hybrid halide perovskite structures, the necessary requirements are favourable geometrical factors (t-factor and octahedral factor) in conjunction with the low ionization energy (ΔHion≤0.2 eV). Two strategies can be used to achieve this goal: (i) find a cation with the low ionization energy or (ii) select an inorganic cage with the low electron affinity. With these information, it becomes possible to help in finding a new stable perovskite material as an active layer for solar cells.
9:00 PM - ES1.5.21
Poly(Methyl Methacrylate) Based Composite Encapsulation for Long-Term Stable Perovskite Solar Cells in Humid Condition
Gill Sang Han 1 , Fangda Yu 1 , Matthew Lawrence Duff 1 , Jung-Kun Lee 1 Show Abstract
1 Department of Mechanical Engineering & Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
In spite of a continuous increase in power conversion efficiency (PCE) and an economically viable fabrication process, organic-inorganic perovskite solar cells (PSCs) have a significant problem to be resolved for commercialization in the photovoltaic industry. The PSCs show a fast degradation of PCE when they are exposed to heat, light, and humid environment. While easy degradation is a pressing and urgent issue, there are relatively few studies on improving the long-term stability of PSCs. In this study, the stability of PSCs under very humid environment is greatly enhanced by coating a poly(methyl methacrylate) (PMMA) – reduced graphene oxide (rGO) composite (PRC) encapsulation layer on the surface of PSC devices. A PMMA-rGO composite creates a hydrophobic surface through interaction between ester group of PMMA and hydrophilic rGO surface. The stability of PSCs using PRC is better than bare PSCs or PSCs with pure PMMA passivation layer. In particular, implementation of the PRC passivation layer into PSCs dramatically suppresses the dissociation of (CH3NH3)PbI3 to (CH3NH3)I and PbI2. This is because the hydrophobic surface prevents adsorption of H2O and the diffusion pathway of H2O, O2 and other gas molecules become more tortuous in PRC. Furthermore, high thermal conductivity of rGO makes heat travel faster in the PRC layer and improves thermal stability of PSCs at 80 oC. As a result, the initial efficiency of PRC coated PSC (~16%) is maintained for 1000 hours in humid environment.
9:00 PM - ES1.5.22
A Surface-Modification Strategy to Prepare Efficient and Stable Perovskite Solar Cells in Ambient Air
Chang Liu 1 , Xianyong Zhou 1 , Chun Cheng 1 , Baomin Xu 1 Show Abstract
1 Materials Science and Engineering, South University of Science and Technology, Shenzhen China
Among many photovoltaic conversion technologies, perovskite solar cells have received significant research interests as effective photovoltaic materials due to their high solar conversion efficiencies and low cost. However, the performance of perovskite solar cell is limited by the instability of CH3NH3PbI3 to water and ambient moisture. To address this issue, we introduce a new fundamental approach that utilizes 4-tert-butylpyridine (tBP) as surface modification agent to enhance the performance and stability of CH3NH3PbI3-based perovskite solar cells. The tertiary butyl contained in tBP is a high hydrophobic group, which leads to a hydrophobic layer formatting on the surfaces of CH3NH3PbI3 to promote the moisture stability of perovskite solar cells. With this strategy, the performance of perovskite solar cells prepared in ambient air has been gigantically enhanced by as much as 200%. Besides, the stability of perovskite solar cells in ambient air can be markedly improved. Since this gigantic enhancement of the photoelectric conversion efficiency through tBP addition is universally applicable to any material based perovskite solar cells, the new mechanism and approach will lead to a revolutionary advance of the field towards the goal to fabricate efficient and stable perovskite solar cell devices in ambient atmosphere condition.
9:00 PM - ES1.5.23
Athmospherically Processed and Stable Cs-Pb and Cs-Sn Based Perovskite Solar Cells
Shubhra Bansal 1 , Sarah Thornton 1 Show Abstract
1 , University of Nevada, Las Vegas, Las Vegas, Nevada, United States
Perovskite solar cells have shown dramatic improvement in efficiency from 3.9% to 22.1% in a short span, however, few issues with these materials remain to be addressed for successful commercialization of this promising technology. Sensitivity to atmospheric processing, large degradation rates and toxicity of Pb are a few challenges addressed in our research. Two types of planar heterojunction superstrate n-i-p devices based on Zn(O,S) electron transport layer (ETL) will be reported. Absorber materials CsPbI2Br and Cs2SnI6 with respective bandgaps of 1.9 eV and 1.65 eV are demonstrated via atmospheric solution processing. Thermal anneals at 85 °C and light soaking tests at 65 °C and 1-sun shows the two phases are stable as indicated by X-ray diffraction, UV-Vis and photoluminescence spectroscopy. Devices fabricated with Zn(O,S) electron transport layer and CsPbI2Br absorber show a stabilized efficiency of 11.94% with no hysteresis between forward and reverse scans.The devices show voltage dependent current collection as well as light-dark crossover in forward bias. A chemical bath deposition process is used for Zn(O,S) and a modified 2-steps process for CsPbI2Br, followed by carbon-based hole transport layer (HTL). CsPbI2Br devices exhibit < 25% in 100 hours of light soak tests at 1-sun and 65 °C in air. CsPbI2Br devices degrade due to shunting most likely due to scratching from probes and hot-spot formation. Halide segregation has been previously reported as a degradation mechanism in CsPbI2Br devices, however, upto 100 hours of standard light soak test does not show any halide segregation for our CsPbI2Br films. Further testing is currently underway. The devices exhibit a positive temperature coefficient of about 0.14 %/°C. It is found that Zn(O,S) is a viable alternative electron transport layer to TiO2 to address stability challenges associated with the latter. By replacing methylammonium cation with cesium and addition of Br has improved the stability of the perovskite phase within the practical operational limit for solar cells.
Cs2SnI6 devices have been fabricated as superstrate n-i-p devices Tec 8 glass using Zn(O,S) ETL and carbon-based HTL, albeit with low power conversion efficiency. However, the films exhibit a stable Cs2SnI6 phase with a bandgap of 1.65 eV even after 100 hours anneal at 85 °C in vacuum. Vacuum deposition of Cs2SnI6 has been reported n-type with high ionization potential and electron affinity. This is the first report of atmospherically processed Cs2SnI6 phase with bandgap of 1.65 eV to the best of our knowledge. Future work includes optimization of Zn(O,S) and Cs2SnI6 for improved efficiencydevices, as well as optimization of HTL and upto 100 hours of light soak tests.
9:00 PM - ES1.5.24
The Detrimental Effect of Excess Mobile Ions in Planar CH3NH3PbI3 Perovskite Solar Cells
Yuanhang Cheng 1 , Sai Wing Tsang 1 Show Abstract
1 , City University of Hong Kong, Kowloon Hong Kong
The origin of the impact of mobile ion in perovksite solar cells (PVSCs) has recently become a hot topic under debate. Here, we investigate systematically the structural effect and various recombination pathways in PVSCs with different ion concentrations. By probing the transient ionic current in PVSCs, we extract mobile ion concentrations in a range of 1016 cm-3 to 1017 cm-3 depending on the processing conditions during a two-step process. The PVSC with the lowest ion concentration has both the highest efficiency over 15% and shelf-life over 1300 hours. Interestingly, in contrast to the commonly adopted models in literatures, we find that the crystal size and the bimolecular and trap-assisted recombination are not responsible to the large difference in photovoltaic performance. Instead, by using transient photocurrent and steady-state photoluminescence approaches, we find that the large reduction of short-circuit current (Jsc) in mobile ion populated device is ascribed to the slow decay in photocurrent and the increasing amount of non-radiative recombination. In addition, we also find that the excess mobile ions trigger the deformation of perovskite to PbI2, which severely reduce the device lifetime. The results provide valuable information on the understanding of the role of excess mobile ion on the degradation mechanism of PVSCs.
9:00 PM - ES1.5.25
Investigation of Chemical Structure and Physical Properties of Organic-Inorganic Metal Halide Materials for Solid State Solar Cells
Majid Safdari 1 Show Abstract
1 , Royal Institute of Technology, Stockholm Sweden
Methylammonium lead iodide has recently attracted tremendous interests which may results in monumental leap in development of efficient and inexpensive photovoltaics. The application of this material as light absorbing layer in solid state solar cells leads to impressive efficiency of over 22% for laboratory devices. However, fundamental questions regarding their thermal and moisture stability need to be addressed. MAPbI3 is from perovskite family of materials with general formula of ABX3. A is the organic cation (methylammonium) which is reported as one major source for instability. In my PhD thesis, I have synthesized different variety of alkyammonium lead iodide by changing the organic cation to study the correlation between the structural and physical properties of these materials. Methylammonium, ethylammonium and propylammonium were used for (APbI3) series. For dAPbI4, dialkylammonium of butyldiammonium, hexyldiammonium, and octyldiammonium were applied. Variant dimensionality from three dimensional (3D) networks (MAPbI3, MAPbBr3), two dimensional (2D) layered systems (BdAPbI4, HdAPbI4, OdAPbI4), and one dimensional (1D) columns (EAPbI3, PAPbI3, EAPb2I6) were observed for these materials. Several new lower dimensional materials (2D and 1D) were investigated for the first time. X-ray single crystallography was used to obtain the detailed strutural properties of the products. Bulk structures were confirmed by comparison of the X-ray diffraction patterns with the single crystal data. [PbI6] octahedral structural unit were found for the materials which based on the dimensionality and connectivity of the materials are repeated through the material’s network. By introducing bulkier cation to the material, the crystallographic unit cell increased in size which yielded lower symmetry crystals for the products. Corner-shared and phase-shared systems were found for the different products. Lower dimensionality resulted in higher bandgap, lower photoconductivity, hence lower light conversion efficiency for the related solar cells. Enhanced thermal and moisture stability were found for the 1D and 2D materials. Electronic structure of the new 2D layered perovskites thoroughly investigated by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and X-ray emission spectroscopy. Density functional theory calculations were used to calculate band structures, density of states and partial density of states. These findings were in agreement with the experimental part, indicating that valence band is mainly composed of iodine orbitals while lead orbitals are dominating in conduction band. Iodide/lead ratio obtained from surface analysis of the deposited material on the TiO2 films well-matched with the proposed general formula from single crystal data. An overall picture for the impact of the bulkier cation in the physical and structural properties is provided which can be used to design new materials for applications in photoelectrochemical device.
9:00 PM - ES1.5.26
Light-Induced Degradation of Methylammonium and Formamidinium Lead Iodide Perovskites
Norbert Nickel 1 , Felix Lang 1 , Viktor Brus 1 , Joerg Rappich 1 Show Abstract
1 , Helmholtz Zentrum Berlin für Materialien und Energie GmbH, Berlin Germany
For some years organic-inorganic perovskites have attracted great interest due to their outstanding electrical and optical properties. Because of their large absorption coefficient, high carrier mobility, and long carrier diffusion length this class of materials is very attractive for opto-electronic applications such as light emitting devices and solar cells. Perovskite solar cells experienced a remarkable development in recent years. Their power conversion efficiency increased from single digit values to more than 22 %.  Despite of the high power conversion efficiencies organic-inorganic perovskites suffer from a number of instability mechanisms. To improve the stability of perovskite solar cells containing these absorbers a fundamental understanding of the governing mechanisms is advantageous.
In this paper we investigate the stability of methylammonium (CH3NH3+ - MA) and formamidinium (HC(NH2)2+ - FM) lead iodide perovskite films using visible and ultra violet light in oxygen atmosphere and in vacuum. Insight into the degradation mechanisms was obtained from in-situ Fourier-transform infrared absorption (FT-IR), photoluminescence, and gas effusion measurements. We revisited the light-induced degradation of MAPbI3 in the presence of oxygen. Illumination in O2 atmosphere results in a swift degradation. Isotope experiments clearly show that O2 acts as a catalyst decomposing MA ions into CH3NH2 and hydrogen. In case of FMPbI3 perovskites illumination in the presence of O2 results in a more complex reaction; decomposition of the FM ions occurs at the N – C – N bonds and as a result CO2 and C = O molecules are formed that rapidly diffuse out of the crystalline lattice.
In addition, we present experimental evidence of a hitherto unknown but fundamental degradation mechanism of MAPbI3 and FMPbI3 perovskite layers due to exposure to visible and ultra violet light. This degradation mechanism does not require the presence of oxygen or other constituents. Prolonged illumination causes the dissociation of MA ions into molecular hydrogen and CH3NH2. Interestingly, FM ions also decompose into CH3NH2. The resulting molecules are highly mobile at room temperature and diffuse out of the perovskite layer. As a result, the concentration of localized defects increases and quenches the photoluminescence. Our data indicate that the molecular orbitals of the organic ions are not in resonance with the energy bands of the perovskite
 Http://www.nrel.gov/ncpv/images/efficiency_chart.jpg (2016).
9:00 PM - ES1.5.27
Correlations of Optical Absorption, Charge Trapping, and Surface Roughness of TiO2 Photoanode Layer Loaded with Neat Ag-NPs for Efficient Perovskite Solar Cells
Dongwook Yang 1 , Jae Gyu Jang 1 , Sung Hyun Kim 2 , Jong-In Hong 1 Show Abstract
1 Department of Chemistry, Seoul National University, Seoul Korea (the Republic of), 2 Department of Carbon Fusion Technology, Wonkwang University, Iksan Korea (the Republic of)
We systematically investigated the effect of silver nanoparticles (Ag-NPs) on the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Neat, spherical Ag-NPs at loading levels of 0.0 wt%, 0.5 wt%, 1.0 wt%, and 2.0 wt% were embedded into the TiO2 photoanode layer. The plasmonic effect of the Ag-NPs strongly enhanced the incident light absorption over a wide range of the visible wavelength region, in addition to the inherent absorbance of the perovskite sensitizer. The low conduction energy level of the Ag-NPs compared to that of TiO2 provides trap sites for free charge carriers. Thus, the correlation between the enhancement of the optical absorption and the number of charge traps provided by the Ag-NPs is critical to determine the device performance; especially current density (Jsc) and PCE. This is confirmed by the quantitative comparison of the incident light absorption and the time-resolved photoluminescence decay according to the loading levels of the Ag-NPs in the TiO2 layer. The absorption enhancement from 380 to 750 nm in the UV-visible spectrum is proportional to the increase in the loading levels of the Ag-NPs. However, the Jsc increases only with the device with 0.5 wt% Ag-NPs and gradually decreases with increases in the loading level above 0.5 wt% because of the different contributions to the absorbance and the charge trapping by different Ag- NPs loading levels. In addition, the suppression of the surface roughness with dense packing by the Ag-NPs helps to improve the Jsc and the following PCE. Consequently, the PCE of the PSC with 0.5 wt% Ag-NPs is increased to 11.96%. These results are attributed to the balance between increased absorbance by the localized surface plasmon resonance and the decreased charge trapping, as well as the decreased surface roughness of the TiO2 layer with the Ag-NPs.
Yabing Qi, Okinawa Institute of Science and Technology
Wei Huang, Nanjing Tech University
Nam-Gyu Park, Sungkyunkwan University
Kai Zhu, National Renewable Energy Laboratory
Applied Physics Letters | AIP Publishing
The Journal of Physical Chemistry Letters | ACS Publications
National Renewable Energy Laboratory
Nature Energy | Springer Nature
Science Magazine| AAAS
Wiley VCH Verlag GmbH &
ES1.6: Tandem, Mixed Perovskites, Transistor and Carbon Materials
Wednesday AM, April 19, 2017
PCC North, 200 Level, Room 224 B
9:00 AM - ES1.6.01
Cu2O/Al:ZnO as a Tunneling Junction for Perovskite/Si Tandem Solar Cells
Pravakar Rajbhandari 1 , Dallas Fisher 1 , Som Dahal 2 , Tara Dhakal 1 Show Abstract
1 Electrical and Computer Engineering, and Center for Autonomous Solar Power (CASP), Binghamton University, Binghamton, New York, United States, 2 Solar Power Labs, Arizona State University, Tempe, Arizona, United States
In this presentation, we report the performance of transparent tunneling junction Cu2O/Al:ZnO for perovskite/Si tandem solar cell. Al:ZnO has a higher refractive index than that of indium doped tin oxide (ITO), which minimizes optical losses in the tunneling junction. Cu2O is a p-type material whose carrier concentration can be controlled by nitrogen doping. The top cell of the tandem structure, the perovskite solar cell, is fabricated on the bottom silicon solar cell received from the Solar Power Labs at Arizona State University. Here Cu2O is used for two purposes. The moderately doped Cu2O is used as an inorganic hole transport layer for the perovskite, and degenerate nitrogen doped Cu2O is used for the tunnel junction. The efficiency of the perovskite used is in the order of 16% and that of silicon used is 17-19%. The optimization of the tunneling junction is initially tested by sand-witching them between two metal contacts in order to confirm the quality of the tunnel junction. This is then used as the tunneling junction between the well-established high efficiency mixed halide perovskite/Si tandem structure.
9:15 AM - ES1.6.02
Robust Recombination Contacts for Perovskite on p-Type Silicon Tandem Solar Cells
Ian Marius Peters 1 , Robert Hoye 1 , Kevin Bush 2 , Sarah Sofia 1 , Felipe Oviedo 1 , Jonathan Mailoa 1 , Joel Jean 1 , Anna Osherov 1 , Vladimir Bulovic 1 , Michael McGehee 2 , Tonio Buonassisi 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Stanford University, Stanford, California, United States
Tandem solar cells for non-concentrated light are widely considered a promising strategy for reducing the cost-to-power ratio of commercial photovoltaics, by enabling power conversion efficiencies beyond that of conventional single-junction solar cells. Monolithically integrated tandems in particular can achieve lower cost and simpler module operation than four-terminal tandems. For tandem solar cells to be commercially successful, each sub-cell must be produced at low cost . By far the most common photovoltaic technology in the global market today is based on multicrystalline p-type silicon. Hybrid organic-inorganic lead halide perovskite solar cells complement silicon in tandem solar cells, as perovskites can be fabricated with the optimal top-cell bandgap using low-cost solution processing. However, research on perovskite-silicon tandem solar cells has thus far focused on devices employing n-type silicon. N-type silicon offers higher efficiencies but is less industrially common, constituting roughly 5% of the global photovoltaics market. In this work we discuss the steps required to enable perovskite on p-type silicon tandem solar cells, and present a prototype realized with this technology.
The most significant change for a monolithic tandem on p-type silicon is that the polarity of all layers is inverted compared to tandems on n-type silicon . This inversion necessitates the development of a new recombination contact between the silicon solar cell’s electron collector and the perovskite cell’s hole transport layer (HTL). This contact must be stable and protect the bottom cell during top-cell fabrication. Furthermore, the HTL must be highly transparent to near-infrared light, which disqualifies typical HTL materials such as Spiro-OMeTAD. NiOx is a suitable alternative, exhibiting a high near-IR transmittance and enabling higher open-circuit voltages than PEDOT:PSS. To ensure a stable open-circuit voltage under illumination, we found it necessary to minimize moisture on the NiOx surface. We developed a recombination contact between NiOx and sputtered indium tin oxide (ITO), which is compatible with the p-type silicon bottom cell, has a high IR transmittance, and protects the bottom cell from oxidation during top-cell processing. With the NiOx/ITO recombination contact we demonstrate a prototype two-terminal tandem on a p-type silicon solar cell. The prototype had an area of 1 cm2 and a stabilized efficiency of 16%, with a stable open-circuit voltage under one-sun illumination for a 30 min test period. The presented recombination contact could pave the way for the commercial integration of perovskite solar cells with the current dominant material in the global photovoltaics market.
 I M Peters, et al., Techno-economic analysis of tandem photovoltaic systems, RSC Advances 6 (2016), 66911-66923.
 J. P. Mailoa et al., A 2-terminal perovskite/silicon multijunction solar cell enabled by a silicon tunnel junction, APL 106 (2015), 121105.
9:30 AM - *ES1.6.03
Opportunities and Challenges of Mixed Sn-Pb Perovskite Solar Cells
Yanfa Yan 1 Show Abstract
1 , University of Toledo, Toledo, Ohio, United States
Mixed Sn-Pb perovskites not only reduce the usage of toxic Pb, but also provide opportunities for further improvement on power conversion efficiency (PCE) because their bandgaps can be tuned to be more suitable for efficient single-junction solar cell applications. Recently, the PCE of mixed Sn-Pb perovskites has significantly improved, with PCEs as high as more than 15% and open-circuit voltages higher than 800 mV. It is expected that the PCE will continue to increase rapidly. In this talk, I will review the progress of mixed Sn-Pb perovskite solar cells done by ourselves and other groups, and will discuss the potentials and challenges of mixed Sn-Pb perovskite solar cells.
10:00 AM - *ES1.6.04
Compositional and Non-Uniformity Requirements for Commercial Scale Silicon Perovskite Tandem Solar Cells
Christopher Case 1 2 , Edward Crossland 1 Show Abstract
1 , Oxford PV, Begbroke United Kingdom, 2 Physics, University of Oxford, Oxford United Kingdom
With over 2000 technical papers published in 2016 on the use of perovskite materials for photovoltaic applications, many fundamental questions remain as to the actual role and performance of the various thin film layers in typical devices. Oxford PV (OxPV), a University of Oxford spin-out company is endeavouring to commercialise one form of this technology – perovskite on silicon tandem solar cells which have the potential to exceed the conversion efficiency of the highest performing single junction silicon cells. With only two percent of energy generated by PV today and a view of an all-electric future to mitigate global warming, every opportunity to raise efficiency needs to be explored.
Key requirements for a successful PV technology are of course the manufacturing robustness of the process, the economics of the product (at >100MW scale), performance and of course reliability. A complete understanding starting with the fundamental atomic arrangement of the atoms in the material, through the composition and homogeneity of the deposited thin films to the final optimisation of the module based on optical modelling is ideal. In order to accelerate the development, the use of appropriate models and theoretical calculations that can predict or support the understanding of the various changes in the intrinsic material and its interactions with the surrounding layers is valuable. OxPV collaborates with many research and industrial groups and works with supplier partners to broaden its understanding of these solar cells.
We will report on some of our findings on non-uniformity at the nano-scale and with high spatial resolution, through the use of characterisation techniques such as RBS, neutron diffraction, nano-scale FTIR, electron microscopy and optical modelling and theoretical calculations. These techniques, along with computational screening, have allowed us to create a reliable and stable device. Long term test data based upon the IEC61646 suite of tests will be presented. Optical models will be used to highlight the annualised energy yield of tandem modules. We will also report on cost of ownership (CoO) models that validate the commercial business case for these silicon perovskite tandem solar cells and provide a roadmap for future products.
10:30 AM - ES1.6.05
23.6%-Efficient Monolithic Perovskite/Silicon Tandem Solar Cells with Improved Stability
Kevin Bush 4 , Axel Palmstrom 4 , Zhengshan Yu 1 , Mathieu Boccard 1 , Rongrong Cheacharoen 4 , Jonathan Mailoa 3 , David McMeekin 2 , Robert Hoye 3 , Colin Bailie 4 , Tomas Leijtens 4 , Ian Marius Peters 3 , Maxmillian Minichetti 4 , Rohit Prasanna 4 , Sarah Sofia 3 , Henry Snaith 2 , Tonio Buonassisi 3 , Zachary Holman 1 , Stacey Bent 4 , Michael McGehee 4 Show Abstract
4 , Stanford University, Stanford, California, United States, 1 , Arizona State University, Tempe, Arizona, United States, 3 , Massachusetts Institute of Technology, Boston, Massachusetts, United States, 2 , University of Oxford, Oxford United Kingdom
As the record single-junction efficiencies of perovskite solar cells now rival those of CIGS, CdTe, and multicrystalline silicon, they are becoming increasingly attractive for use in tandem solar cells, due to their wide, tunable bandgap and solution processability. This presents a pathway to achieving industry goals of improving efficiencies to over 30% while maintaining low module cost. Of the two main architectures for perovskite/silicon tandems, the four-terminal, mechanically stacked tandem has seen the largest success, recently reaching over 23% with a 1cm2 aperture area , as the architecture requires no current matching. Monolithic perovskite/silicon tandems should benefit from fewer optical losses in electrodes; however, their efficiency continues to lag behind largely due to difficulties in depositing a window layer with high optical transmission [1,2,3].
In addition to being highly transparent, the window layer should act as a buffer layer that protects the perovskite and organic carrier extraction layers from damage during the sputter deposition of a transparent conducting electrode. The ideal buffer layer should also be energetically well aligned to act as a carrier-selective contact, and have no reaction with the halides in the perovskite. Additionally, this buffer layer should act as a diffusion barrier layer to prevent both organic cation evolution and moisture penetration to overcome the often-reported thermal and environmental instability.
This talk will present a new atomic layer deposited tin oxide window layer close to this ideal, with minimal parasitic absorption and effective sputter buffer properties enabling the deposition of a transparent indium tin oxide electrode. With this window layer, a 1.6 eV band gap CsyFA1-yPb(BrxI1-x)3 perovskite, and a heterojunction silicon cell optimized for performance in the near-IR, we achieved NREL certified record 23.6% efficient monolithic perovskite/silicon tandems with a 1cm2 aperture area. We will explain in detail how the tandem structure was designed and present analysis on what needs to be done to achieve 30% efficiency. Substantial progress towards this goal is likely to be made before the conference.
The devices also show significantly improved maximum power stability under 1-sun illumination, operating continuously for over 1000 hours with minimal degradation. Finally, we fully package our devices with the traditional EVA and glass encapsulation used for silicon solar cells, enabling, for the first time, perovskite devices that do not lose measurable efficiency after a 1000-hour damp heat test at 85°C and 85% relative humidity. This combination of improved efficiency and stability represents a substantial step forward in achieving commercially viable perovskite tandems.
 B. Niesen et al., IEEE-PVSC Conference Proceedings (2016).
 J. Mailoa et al., Applied Physics Letters (2015), 106, 121105.
 K. Bush et al., Advanced Materials (2016), 28, 3937-3943.
11:15 AM - *ES1.6.06
Halide Ion Migration and Charge Carrier Recombination in Mixed Halide Perovskite Films
Seog Yoon 1 , Jacob Hoffman 1 , Prashant Kamat 1 Show Abstract
1 , University of Notre Dame, Notre Dame, Indiana, United States
Mixed halide lead perovskites offer a convenient means to tune the bandgap of the photoactive films. An interesting property of such mixed halide lead perovskites (e.g.,CH3NH3PbI3-xBrx) is phase segregation to create Iodine-rich and Bromide- rich regions when subjected to visible irradiation. This intriguing aspect of halide ion movement in these mixed halide films can be tracked from the changes in the photoluminescence and absorption spectra. Excess halide ions present in the film strongly influence the kinetics of segregation. The charge carriers in the graded CsPbBrxI3-x films have seen to be transferred to iodide rich regions near the film surface within the first several picoseconds after excitation. This ultrafast vectorial charge transfer process illustrates the potential of utilizing compositional gradients to direct charge flow in perovskite based photovoltaics.
11:45 AM - ES1.6.07
Liquid Water- and Heat-Resistant Hybrid Perovskite PV via an Inverted ALD Oxide Design
Alex Martinson 1 , In Soo Kim 1 , Duyen Cao 2 , D. Buchholz 2 , Jonathan Emery 2 , Omar Farha 2 , Mercouri Kanatzidis 2 , Joseph Hupp 2 Show Abstract
1 , Argonne National Laboratory, Argonne, Illinois, United States, 2 , Northwestern University, Evanston, Illinois, United States
Despite rapid advances in conversion efficiency, the environmental stability of perovskite solar cells remains a substantial barrier to commercialization. Here, we show a significant improvement in the stability of inverted perovskite solar cells against liquid water and high operating temperature (100 °C) by integrating an amorhpous oxide electron transport layer via atomic layer deposition (ALD). These inverted devices exhibit stable operation over at least 10 hours when subjected to high thermal stress (100 °C) in ambient environments, as well as in direct contact with a droplet of water without further encapsulation. An inverted ALD oxide design provides a simple and integrated approach to assembling hybrid perovskite solar cells that are more resistant to the environmental stress of high temperature and liquid water. The conformal, amorphous oxide overlayer serves a dual role as both effective diffusion barrier and efficient charge transport layer.
12:00 PM - ES1.6.08
Advances in Stacked Cu(In,Ga)Se2-Perovskite Tandem Solar Cells
Erik Ahlswede 1 , Jonas Hanisch 1 , Moritz Schultes 1 , Tina Wahl 1 Show Abstract
1 , ZSW, Stuttgart Germany
Due to their high energy band gap, perovskite solar cells open the possibility to boost the efficiency of conventional low-bandgap solar cells in a tandem configuration to allow a better utilization of the full sun spectrum by reducing thermalization losses. From a cost perspective the combination of perovskites with thin film technologies is especially appealing, with Cu(In,Ga)Se2 (CIGS) demonstrating the highest potential. Recent advances in the development of stacked tandems of thin-film in combination with semitransparent perovskite solar cells will be presented. Different routes and architectures for efficient semitransparent perovskite cells with only little hysteresis have been studied. Especially the so called inverted structure was investigated with growing interest in the last years because of its simple and low-temperature fabrication process and a potentially better suppression of hysteretic behavior compared to the standard architecture. Furthermore, for the implementation of a perovskite cell in a monolithically stacked 2-terminal tandem device on top of a Cu(In,Ga)Se2 solar cell the inverted semitransparent structure is necessary as well. Hence, our investigation focuses on inverted device development with respect to different front and back contact layers. Low-temperature sputtered transparent front contacts are of particular importance and interest and can be well implemented by taking care about possible (detrimental) influences on the underlying layer stack. The investigated contacts based on In2O3:ZnO (IZO) allow good quality conductive layers without additional heating during the sputter process so that damaging of the perovskite layer can be minimized and a well efficient (>12%) semitransparent cell can be achieved. 4-terminal tandem devices have been realized by optimizing both the CIGS bottom cell and the perovskite top cell reaching efficiencies close to 20% for the stacked device.
12:15 PM - ES1.6.09
Perovskites with Band Gaps Approaching 1.2 eV to Enable Perovskite–Perovskite Tandem Solar Cells
Tomas Leijtens 1 , Giles Eperon 2 , Kevin Bush 1 , Rohit Prasanna 1 , Henry Snaith 2 , Michael McGehee 1 Show Abstract
1 , Stanford University, Stanford, California, United States, 2 , Oxford University, Oxford United Kingdom
Here, we explore the use of small gap perovskite materials based on binary mixtures of lead and tin, focusing on their application in all-perovskite tandem solar cells. By tuning the A and B site composition of the ABX3 perovskite structure and developing a new processing route to form smooth continuous films, we are able to make highly efficient (14.8 %) planar heterojunction solar cells with small (~ 1.2 eV) bandgaps, suitable for all-perovskite tandem solar cells. Previous reports of tin based perovskite solar cells have demonstrated these to be extremely unstable under operation and in air. We find that our mixed perovskite is remarkably stable, showing no signs of degradation under operation in air for over an hour, and find an interesting dependence on Sn:Pb ratio in terms of stability. It has also been difficult to solution process two perovskite cells on top of one another to make monolithic tandems without dissolving the underlying layers. We have overcome this issue by careful selection of the recombination layer. As a result, we have been able to successfully make monolithic all-perovskite solar cells of 17 %, and mechanically stacked all-perovskite tandem solar cells over 20%. The monolithic tandems display remarkable matched photocurrents of close to 15 mA cm-2, demonstrating their great potential. An analysis of the losses and avenues to future improvements will be discussed.
12:30 PM - ES1.6.10
Enhanced Charge Carrier Extraction in Hybrid Organic Metal Halide Perovskite Solar Cells Using Carbon Nanotube Interlayers
Philip Schulz 1 , Anne-Marie Dowgiallo 1 , Rachelle Ihly 1 , Mengjin Yang 1 , Kai Zhu 1 , Jeffrey Blackburn 1 , Joseph Berry 1 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
The ongoing development of hybrid organic inorganic perovskite photovoltaics has revealed that the numerous interfaces in perovskite solar cells (PSC) play crucial roles for device efficiency and stability. Importantly, many critical interfacial properties are still poorly understood, a deficiency that often limits efforts to improve device performance. Carbon nanotubes have been identified as viable transport layer components in high efficient PSC with enhanced cell characteristics. In this talk I will present our most recent results exploring the mechanisms by which carbon nanotubes enable advantageous charge carrier extraction from the absorber layer and how carbon nanotube interlayers can ideally be embedded in the device geometry.
First, we demonstrated in a detailed photoemission spectroscopy study of semiconducting single-walled carbon nanotubes (s-SWCNT) on top of methlyammonium lead iodide (MAPbI3) absorber films that the formation of an interfacial dipole leads to beneficial band bending in the s-SWCNT film. This observed alignment allows for rapid hole extraction at this interface from the absorber onto the s-SWCNT transport layer as seen from the clear spectroscopic signatures of both phases (MAPbI3 and s-SWCNT) in transient absorption spectroscopy.1 Subsequently, we were able to show that this enhanced hole extraction process impacts the kinetics of charge transfer at multiple interfaces within the device stack by unambiguously tracking charge carrier dynamics with a combination of time resolved photoluminescence, transient absorbance and time resolve microwave conductivity measurements.2 Eventually, we showed that integrating a thin s-SWCNT interlayer between the MAPbI3 absorber and a conventional organic hole transport layer leads to a significant improvement of device characteristics and cell performance. In my outlook I will sketch how the ensemble of these studies opens up an avenue to tailor-made charge carrier extraction interlayers for the next generation of transport layers in PSC.
 P. Schulz et al., J. Phys. Chem. Lett. 2016, 7, 418–425
 R. Ihly et al., Energy Environ. Sci. 2016, 9, 1439-1449
12:45 PM - ES1.6.11
Perovskite Solar Cells Based on Mesoscopic Carbon-Electrode Attaining Efficiency 15% with One Step Slow Crystallization Method
Cheng-Min Tsai 1 , Eric Diau 1 Show Abstract
1 , National Chiao Tung University, Hsinchu Taiwan
Due to excellent optical properties and the low-cost device fabrication, the organic-inorganic hybrid solar cells garnered great attention in recent years. Various approaches to fabricate uniform perovskite films with less number of defects emerged, but for commercialization, device performance stability became critical issues for perovskite solar cells (PSC). We developed a simple and high reproducible one step method, slow crystallization (SC), to grow uniform and compact MAPbI3 crystals at room temperature for mesoscopic carbon electrode solar cells free of an organic hole-transport layer. The SC solar cells based on FTO/TiO2/Al2O3/C film structures displayed a superior stability, that still maintain 95% efficiency for more than 4500 hours without encapsulation. Whole experimental process was done at ambient condition and got remarkable power conversion efficiency (PCE) 15.0% on carbon electrode system by using NMP as solvent, which is significantly greater than that of DMF (2.9%), DMSO (1.7%) and GBL (4.5%). To understand the process of crystallization and MAPbI3 crystallinity, optical microscope (OM), scanning electron microscope (SEM), x-ray diffraction (XRD) and the crystal structure fitting were applied here. The crystals were grown completely through mesoporous TiO2/Al2O3 layers by SC method, that showed big crystal sizes and without clear grain boundary. Moreover, the crystals demonstrated preferred orientation of (004) face, this unique preferred orientation of perovskite crystals grown inside mesoscopic film structures have observed and discussed herein for the first time. Kinetics of charge transfer and defect relaxation for the devices were investigated by transient photoluminescence decays. The SC devices average value of PCE as high as 13.9 ± 0.5%, superior than traditional one step thermal annealing (5.2±1.0%) and two steps sequential methods (10.1±0.7%).
ES1.7: LED, Luminescence and Photophysics
Wednesday PM, April 19, 2017
PCC North, 200 Level, Room 224 B
2:30 PM - *ES1.7.01
Luminescent Low Dimensional Organometal Halide Perovskites
Biwu Ma 1 2 3 , Zhao Yuan 1 , Chenkun Zhou 1 , Yu Tian 3 Show Abstract
1 Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Tallahassee, Florida, United States, 2 Chemistry and Biochemistry, Florida State University, Tallahassee, Florida, United States, 3 Materials Science and Engineering, Florida State University, Tallahassee, Florida, United States
Organometal halide perovskites, consisting of a wide range of inorganic anions and organic cations, are an important class of hybrid crystalline materials with exceptional structural tunability. By choosing appropriate inorganic and organic components, the crystallographic structures can be finely controlled with the inorganic units, i.e. metal halide octahedrons (MX6), forming zero- (0D), one- (1D), two- (2D), and three-dimensional (3D) structures in the hybrids. The integration of useful functionalities from both inorganic and organic realms within a single bulk assembly hybrid affords unique electronic, magnetic, and optical properties. The applications of these materials in optoelectronic devices have been extensively explored in recent years, including photovoltaic cells (PVs), light emitting diodes (LEDs), and optically pumped lasers. Despite tremendous work conducted on various types of hybrid perovskites, the focus has been mainly on 3D and 2D structures containing layer(s) of corner sharing metal halide octahedrons. 1D structures with the metal halide octahedrons connected in a chain and 0D structures with the metal halide octahedrons completely isolated from each other have not been well explored yet. In this talk, I will present our recent efforts in developing and studying new classes of 1D and 0D organometal halide perovskites, which can be considered as bulk assemblies of core-shell quantum wires and quantum dots respectively. Due to the strong quantum confinement, these low dimensional organometal halide perovskites exhibit unique photophysical properties, distinct from those of 2D and 3D counterparts. For instance, highly luminescent broadband emissions with quantum efficiencies of up to near-unity have been realized for these bulk quantum materials, as a result of efficient exciton self-trapping (or excited state structural reorganization). The use of these luminescent bulk quantum materials as light emitter in optoelectronic devices will be discussed.
3:00 PM - ES1.7.02
Excitonic Optical Responses of CH3NH3PbCl3 Single Crystals Revealed by Multi-Photon Excitation Spectroscopy
Takumi Yamada 1 , Yumi Nakaike 1 , Atsushi Wakamiya 1 , Yoshihiko Kanemitsu 1 Show Abstract
1 , Kyoto University, Kyoto Japan
Lead-halide perovskites MAPbX3 (MA = CH3NH3+, X = I-, Br-, Cl-) have been attracting much attention as a new class of materials for photovoltaic and optoelectronic devices. In particular, remarkable progress has been made in thin-film solar cells based on perovskite MAPbI3; their power conversion efficiencies already exceed 20%. High performances of perovskite solar cells are due to superior optical properties of the perovskite layer such as large absorption coefficients, long-lived free-carriers, and large carrier diffusion lengths [1,2]. Further understanding of the fundamental optical properties of MAPbX3 perovskites is needed to improve the performance of optoelectronic devices. To reveal their intrinsic material properties, it is useful to conduct experiments on single crystal samples. With respect to the design of new optoelectronic devices in the blue spectral region, the study of the wide gap material MAPbCl3 is important, especially since only a few studies on MAPbCl3 have been reported so far.
In this study, we investigate the optical properties of MAPbCl3 single crystals. Based on the reflection spectrum, the band edge is determined to be around 3.1 eV. Photoluminescence (PL) and PL excitation (PLE) measurements are conducted under one- and two-photon excitation. The observed PL peak energy under two-photon excitation is lower than that for one-photon excitation due to photon recycling, similar to other MAPbX3single crystals [2-4]. The one-photon PLE spectrum shows a distinct peak around 3.08 eV. On the other hand, the two-photon PLE onset appears at 3.1 eV, which agrees with the band-gap energy. Considering the selection rule for the electric dipole transition, the peak of the one-photon PLE should correspond to the absorption of the 1s exciton. We also measure the time-resolved PL decays for one- and two-photon excitation. Under weak excitation condition, a very fast decay component with lifetime of about 20 ps, and a long decay component on the order of tenths of nanoseconds are observed. The dynamical behavior of the fast decay component suggests an excitonic recombination process. On the other hand, the long decay component is assigned to band-to-band recombination. It is surprising that the free-carrier band-to-band recombination dominates the PL dynamics after the initial fast exciton recombination, which is in contrast to the dynamics observed in MAPbI3 . The details of photocarrier dynamics and excitonic features in MAPbCl3 single crystals are discussed.
Part of this work was supported by CREST, JST.
 Y. Yamada et al., J. Am. Chem. Soc. 136, 11610–11613 (2014).
 Y. Yamada et al., J. Am. Chem. Soc. 137, 10456–10459 (2015).
 T. Yamada et al., Adv. Electron. Mater. 2, 1500290 (2016).
 T. Yamada et al., Phys. Rev. Applied 7, 014001 (2017).
3:15 PM - ES1.7.03
Electrical Stress Improves the Efficiency of CH3NH3PbI3 Perovskite Light Emitting Devices
Lianfeng Zhao 1 , Jia Gao 1 , Kyung Min Lee 1 , Lynn Loo 1 , Barry Rand 1 Show Abstract
1 , Princeton University, Princeton, New Jersey, United States
Organic-inorganic hybrid perovskite materials are emerging as semiconductors with potential application in optoelectronic devices. The past five years have witnessed rapid progress of metal halide perovskite solar cells with power conversion efficiencies rising from 3.8% to over 22%. As an excellent photoactive material, perovskites are also being considered as promising light emitters with high color purity, low non-radiative recombination rates, and tunable bandgap.
Here, we report that the performance of perovskite LEDs can be enhanced by electrical stress. An increase of external quantum efficiency by 25%, from 5.9% to 7.4%, is demonstrated for CH3NH3PbI3 (MAPbI3) perovskite LEDs via multiple electrical scans. Consistent with the enhanced device performance, after multiple electrical scans, the steady-state photoluminescence (PL) intensity within the device structure is increased by ~4 times and time-resolved PL measurements show that the average decay lifetime increases from 0.35 μs to 1.05 μs, indicating a reduction in non-radiative recombination in the perovskite film. By investigating the temperature dependent characteristics of the perovskite LEDs, we find that device efficiency is improved with electrical stress at 260 K and 300 K. However, no performance enhancement is observed at 180 K and 220 K, which appears to be due to the impeded motion of ionic species at lower temperatures. Based on these observations, we propose that, within the as-produced perovskite film, and especially at grain boundaries, iodine vacancies (undercoordinated lead sites) with associated interstitial iodide ions generate a large trap population that serve as non-radiative recombination sites. Upon applying a voltage bias, the increased electric field aids ionic motion, filling vacancies and reducing interstitial defects. As a result, after applying the electrical stress, EL efficiency, PL intensity, and PL lifetime all increase. Furthermore, the enhanced EQE maintains >95% of its value after 3 days in N2, and can be maintained for an extended period of time providing electrical stress is periodically applied.
4:45 PM - *ES1.7.04
NiOx Electrode Interlayer and Methylamine/Perovskite Gas-Solid Treatment to Markedly Advance Hybrid Perovskite-Based Light-Emitting Diodes
Tzung-Fang Guo 1 , Yi-Kai Chih 1 , Jian-Chih Wang 1 , Rei-Ting Yang 1 , Yu-Ching Huang 2 , Cheng-Si Tsao 2 , Chi-Ching Liu 3 , Yun-Chorng Chang 3 , Yaw-Shyan Fu 4 , Wei-Chi Lai 1 , Peter Chen 1 , Ten-Chin Wen 5 Show Abstract
1 Department of Photonics, National Cheng Kung Univ, Tainan Taiwan, 2 Institute of Nuclear Energy Research, Atomic Energy Council, Taoyuan Taiwan, 3 Research Center for Applied Science, Academia Sinica, Taipei Taiwan, 4 Department of Greenergy Technology, National University of Tainan, Tainan Taiwan, 5 Department of Chemical Engineering, National Cheng Kung University, Tainan Taiwan
This work presents the efficient methylammonium lead bromide (CH3NH3PbBr3)-based hybrid light-emitting diodes (LED) of a brightness >70,000 cd/m2 and the luminous efficiency (LE) >15 cd/A. Firstly, the commonly used PEDOT:PSS hole transport layer (HTL) has to be replaced by a more suitable electrode interlayer, such as a compact nickel oxide (NiOx) layer in this study. CH3NH3PbBr3 forms a shiny film on glass/ITO/NiOx substrate and to some extent NiOx layer blocks the transport of the electrons in CH3NH3PbBr3 reaching the electrodes to increase the probabilities for the recombination of opposite charge carriers in the active layer. Secondly, we successfully apply a moderate gas-solid reaction to treat CH3NH3PbBr3 film. The methylamine (MA) treatment promotes the re-growth of CH3NH3PbBr3 crystallites on NiOx layer following the preferred orientations and significantly advances the quality, the crystallinity, photoluminescence of the perovskite film and endorses a more than 100-fold increase in brightness and LE as compared to those of the controlled cell without MA treatment. A hybrid perovksite-based LED with a configuration of glass/indium-tin-oxide/NiOx/MA treated CH3NH3PbBr3/1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBI)/LiF/Al, exhibits a peak LE of 15.9 cd/A biased at 8.5 V, 407.65 mA/cm2, 65,300 cd/m2, posing a feasible gas-solid interaction to largely improve the performance and the design of the highly bright and efficient perovskite-based LEDs for real applications.
5:15 PM - ES1.7.06
Quantitative Correlation of Perovskite Film Morphology to Light Emitting Diodes Efficiency Parameters
Dinesh Kabra 1 , Naresh Kumawat 1 , Nakul Jain 1 , Amrita Dey 1 , K. L. Narasimhan 1 Show Abstract
1 , IIT Bombay, Mumbai India
Growing interest in lighting application after tremendous success in photovoltaics is an obvious move by perovskite semiconductor community with well-known physical concept of “good absorbers are good emitters”. However, perovskite light emitting diodes (PeLEDs)[1,2] have not been able to make similar level progress as compare to solar cells. In this paper, we report quantitative correlation of CH3NH3PbBr3 (MAPbBr3) thin film morphology to light emitting diode efficiency parameters. Sequential (spin coating) deposition is used for highly reproducible and dense film morphology of MAPbBr3 thin-film. In this fabrication process using an orthogonal solvent approach we demonstrate control on morphology, coverage, thickness and optical properties in these compact thin-films. Optical studies showed direct correlation between morphology to dynamics of photoluminescence and absolute PL yield. PeLEDs are fabricated from these films to find the best ratio of PbBr2 vs MABr for optimal performance. We demonstrate PeLEDs with high brightness ~ 4000 cd/m2 at 4.7 V (luminance efficiency » 0.4 cd/A) for optimal thin-film process with state of art device performance. Our quantitative analysis suggested that these state of art PeLEDs suffer from poor charge carrier balance (~2%) and out-coupling efficiency (~6%). Interestingly, charge carrier balance and PL yield together could explain the change in PeLED efficiency modulation with film morphology. Studies on single carrier devices shows that these PeLEDs are electron current dominated and charge carrier balance increases with operating bias voltage.
 “Near infrared to visible electroluminescent diodes based on organometallic halide perovskites: Structural and optical investigation” N. K. Kumawat, A. Dey, K. L. Narasimhan, D. Kabra ACS Photonics Vol. 2, pp-349 (2015)
 “Band Gap Tuning of CH3NH3Pb (Br1–x Cl x) 3 Hybrid Perovskite for Blue Electroluminescence” N. K. Kumawat, A. Dey, A. Kumar, S. P. Gopinathan, K. L. Narasimhan, D. Kabra ACS Appl. Mat. & Inter. Vol. 7, pp- 13119 (2015)
 “Quantitative Correlation of Perovskite Film Morphology to Light Emitting Diodes Efficiency Parameters” N. K. Kumawat, N. Jain, A. Dey, K. L. Narasimhan, D. Kabra Adv. Func. Mater. (2016) (DOI: 10.1002/adfm.201603219)
5:30 PM - ES1.7.07
Liquid-Like Screening in Hybrid Perovskites—A Hierarchical Charge Protection Mechanism
Kiyoshi Miyata 1 , Haiming Zhu 1 , Tuan Trinh 1 , Yongping Fu 2 , Jue Wang 1 , Prakriti Joshi 1 , Daniel Niesner 1 , Kristopher Williams 1 , Song Jin 2 , Xiaoyang Zhu 1 Show Abstract
1 Chemistry, Columbia University, New York, New York, United States, 2 Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States
Hybrid lead halide perovskites demonstrate carrier properties that rival those of defect-free nonpolar semiconductors in spite of unavoidable defects, suggesting that carriers are protected from scattering with optical phonons and charged defects. Here, we look into the carrier protection mechanism by comparing three single-crystal lead bromide perovskites: hybrid perovskites, CH3NH3PbBr3, CH(NH2)2PbBr3, and their all-inorganic counterpart, CsPbBr3. We observed hot fluorescence emission from energetic carriers with ~102-picosecond lifetimes in CH3NH3PbBr3 or CH(NH2)2PbBr3, but not in CsPbBr3 at room temperature. The hot fluorescence is correlated well with liquid-like structural response observed by time-resolved optical Kerr effect spectroscopy, suggesting that dynamic screening of the Coulomb potential on time scales competitive with cooling via LO-phonon scattering. This screening dynamics resemble solvation dynamics of a charge in a polar liquid. In contrast to hot carriers, we find similar physical properties in band edge carriers among the three perovskites, including slow carrier trapping, low surface recombination velocity, low radiative recombination rate, and modest carrier mobility regardless of cation type. Because the lifetimes of the band edge carriers are long enough to be screened by the soft PbBr6- lattice motion, the protections for band edge carriers are present in both hybrid and all-inorganic perovskites. These comparative studies elucidate the role of the motions of both organic cations and inorganic octahedral lattices on the screening of charge carriers in lead halide perovskite lattices.
 Zhu, H. et al. “Screening in crystalline liquids protects energetic carriers in hybrid perovskites,” Science, 2016, 353, 1409-1413
 Zhu, H. et al. “Organic cations might not be essential for the exceptional properties of bandedge carriers in lead halide perovskites,” Adv. Mater. 2016, 28, in press
5:45 PM - ES1.7.08
Real-Time Observation of Iodide Ion Migration and Its Influence on Hysteresis in Methylammonium Lead Halide Perovskites
Cheng Li 1 , Yu Zhong 1 , Sven Huettner 1 Show Abstract
1 , University Bayreuth, Bayreuth Germany
Organic-inorganic metal-halide perovskites (e.g. CH3NH3PbI3-xClx) emerged as a promising opto-electronic material. However, the Shockley–Queisser Limit for the power conversion efficiency (PCE) of perovskite-based devices has still not been reached, which was attributed to non-radiative recombination pathways, as suggested by photoluminescence (PL) inactive (or dark) areas on perovskite films. Although these observations have been related to the presence of ions/defects, the underlying fundamental physics and detailed microscopic processes, concerning trap/defect status, ion migration, etc., still remain poorly understood. Here we utilize correlated time resolved PL microscopy and impedance spectroscopy (IS) on perovskite films to in-situ investigate both the spatial and temporal evolution of these PL inactive areas under external optical/electrical fields. We attribute the formation of PL inactive domains to the migration and accumulation of iodine ions under external fields. Our approach, therefore, enables to characterize the kinetic processes and determine the mobility of these ions. In addition, we fabricate perovskite solar cells incorporating phenyl-C61-butyric acid methyl ester (PCBM) and PCBM polymer to investigate the influence of diffusions of PCBM molecules on the hysteretic behavior. By employing the PL imaging microscopy, we in-situ visualize the migration of iodide ions under external electrical field. Comparison of three systems: (1) single perovskite layer (2) perovskite/PCBM bilayer (3) mixed perovskite/PCBM bulk heterojunction, indicates the decrease of migration speed when involving PCBM molecules. Following that, the step-wise temperature dependent J-V curve measurement further demonstrates the reduction of migration and increase of activation energy with the aid of PCBM molecules. Hence, it is proposed that the elimination/alleviation of J-V curve hysteresis is ascribed to the diffusion of PCBM molecules, which passivate the iodide related defects and form PCBM-halide radical. This formation significantly reduces the iodide ion migration, leading to the reduction of modulation in built-in field and interfacial barriers in devices.
ES1.8: Poster Session II
Thursday AM, April 20, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ES1.8.01
Ferroelasticity in MAPbI3
Tao Li 1 , Yuchuan Shao 1 , Yehao Deng 1 , Andrea Centrone 2 , Jinsong Huang 1 , Alexei Gruverman 1 Show Abstract
1 , University of Nebraska–Lincoln, Lincoln, Nebraska, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Organic perovskites CH3NH3PbI3 (MAPbI3) are promising materials for the next generation of solar cells as they show high power conversion efficiency. Ferroelectricity has been proposed as a plausible mechanism to explain this feature of organic perovskites. However, convincing experimental evidence in support to this hypothesis is still missing. Nevertheless, our recent Piezoresponse Force Microscopy studies demonstrate solid evidence of the ferroelastic domains of pristine and stressed MAPbI3 polycrystalline films. These ferroelastic domains can be manipulated by externally applied stress. This suggests that strain engineering may be an alternative way to tune the materials properties. In addition, the temperature and illumination effects on changing the ferroelastic domains have been evaluated. Observation of the ferroelastic behavior of MAPbI3 may shed new light on the organic perovskites unique photovoltaic properties.
9:00 PM - ES1.8.02
Mobility-Lifetime Products in MAPbI3 Films
Igal Levine 1 , Satyajit Gupta 1 , Thomas Brenner 1 , Doron Azulai 2 , Oded Millo 2 , Gary Hodes 1 , David Cahen 1 , Isaac Balberg 2 Show Abstract
1 , Weizmann Inst of Science, Rehovot Israel, 2 , The Hebrew University, Jerusalem Israel
Photovoltaic solar cells are based on the steady state that is established during the charge carrier excitation and recombination. However, hitherto no model of the steady state recombination scenario in the Halide Perovskites has been proposed. We present such a model that is based on a single type of recombination center, which is deduced from our measurements of the illumination intensity dependence of the photoconductivity and the ambipolar diffusion length in those systems. We also discuss the relation between the present results and those from time-resolved measurements, such as photoluminescence that are commonly reported in the literature.
9:00 PM - ES1.8.03
Origin of Long Lifetime of Band-Edge Charge Carriers in Organic-Inorganic Lead Iodide Perovskites
Tianran Chen 1 , Wei-Liang Chen 2 , Benjamin Foley 3 , Jooseop Lee 4 , Jacob Ruff 4 , J.Y. Peter Ko 4 , Craig Brown 5 , Leland Harriger 5 , Depei Zhang 1 , Changwon Park 6 , Mina Yoon 6 , Yu-Ming Chang 2 , Joshua Choi 3 , Seung-Hun Lee 1 Show Abstract
1 Department of Physics, University of Virginia, Charlottesville, Virginia, United States, 2 Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, 3 Department of Chemical Engineering, University of Virginia, Charlottesville, Virginia, United States, 4 Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, United States, 5 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 6 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Long carrier lifetime is what makes hybrid organic-inorganic perovskites high performance photovoltaic materials. Several microscopic mechanisms behind the unusually long carrier lifetime have been proposed, such as formation of large polarons, Rashba effect, ferroelectric domains, and photon recycling. Here, we show that the screening of band-edge charge carriers by rotation of organic cation molecules can be a major contribution to the prolonged carrier lifetime. Our results reveal that the band-edge carrier lifetime increases when the system enters from a phase with lower rotational entropy to another phase with higher entropy. These results imply that the recombination of the photo-excited electrons and holes is suppressed by the screening, leading to the formation of polarons and thereby extending the lifetime. Thus, searching for organic-inorganic perovskites with high rotational entropy over a wide range of temperature may be a key to achieve superior solar cell performance.
9:00 PM - ES1.8.04
Influence of Ferroelectric Polarization on Photo-Conversion Efficiency of Hybrid Perovskite Absorber Solar Cells
Hye Ri Jung 1 , Phuong Nguyen 1 , Juran Kim 1 , Hye-Jin Jin 1 , William Jo 1 Show Abstract
1 Department of Physics, Ewha Womans University, Seoul Korea (the Republic of)
Hybrid lead halide perovksite, MAPbX3(MA=CH3NH3+, X=Br- or I-) emerged with remarkable efficiency increasing and examination on its physical properties are of particular concern. One of the issues is hysteresis phenomenon. Current-voltage curves differ depending on the sweep rate and direction. Several mechanisms have been proposed including difference in trapping efficiency, ion migration, imbalance between electron and hole fluxes into an electron transfer layer and a hole transfer layer, and ferroelectricity of the perovskites. We report our observations on the polarization in the thin films by measuring piezoelectric responses and ferroelectric property using piezoelectric force microscopy which is one of atomic force microscopy techniques. In addition, we verify the details of the crystal structure in terms of configuration of the Methylammonium ligands. We propose a device model to enhance charge transfer in the perovskite solar cells when we have a preferred polarization in the materials.
9:00 PM - ES1.8.05
Alkali Metal Halide Salts as Interface Additives to Fabricate Hysteresis-Free Hybrid Perovskite-Based Photovoltaic Devices
Lili Wang 1 , Dhanashree Moghe 1 , Soroush Hafezian 2 , Pei Chen 1 , Margaret Young 1 , Mark Elinski 1 , Ludvik Martinu 2 , Stephane Kena-Cohen 2 , Richard Lunt 1 Show Abstract
1 , Michigan State University, East Lansing, Michigan, United States, 2 , Polytechnique Montreal, Montréal, Quebec, Canada
Understanding defects and interfaces is key challenge in fully optimizing hybrid perovskite-based photovoltaics to minimize hysteresis, enhance performance, and extend lifetime. In this work a new approach is developed to dope alkali metal halide salts as interface additives to fabricate hysteresis-free hybrid perovskite-based photovoltaic devices. By decoupling the dopant from the perovskite precursors, these metal halide compounds are shown to be viable dopants for this new class of photovoltaics. The best performance of methylammonium lead mixed halide perovskite device was achieved with a NaI interlayer and showed a PCE of 13% and a hysteresis of less than 2%, representing a 90% improvement compared to control devices without this salt. Ultimately, a range of solution-processed halide salts with various cation or anion were investigated. Depth-resolved mass spectrometry, optical modeling and photoluminescence spectra were used to uncover the role of such doping. The enhancements from NaI doping are ultimately attributed to multiple synergistic mechanisms including the reduction of iodide vacancies, passivation of grain boundaries and improved hole extraction. This approach could lead to routes to controllable and multi-interface doping profiles, and provide a new strategy for the doping of a wide range of perovskite devices.
9:00 PM - ES1.8.06
Free Excitons and Exciton–Phonon Couplings in Orthorhombic-Phase CH3NH3PbI3 Single Crystals
Le Phuong 1 , David Tex 1 , Hirokazu Tahara 1 , Yumi Nakaike 1 , Atsushi Wakamiya 1 , Yoshihiko Kanemitsu 1 Show Abstract
1 , Institute for Chemical Research, Kyoto University, Kyoto Japan
Organic-inorganic metal halide perovskites, such as CH3NH3PbX3 (MAPbX3, X = I, Br, Cl), provide an outstanding class of materials for various optoelectronic applications such as solar cells, light-emitting diodes, and lasers . In spite of recent comprehensive studies, knowledge of the exciton characteristics in MAPbX3 perovskites is still limited due to the divergent interpretations  originated most likely from the use of polycrystalline thin films, which comprise grains with varying size and composition. Thus, studies of single crystals are needed to gain insights of the exciton properties. However, the widely used spectroscopic techniques, for instance, absorption measurement, are not applicable to thick macroscopic single crystals. On the other hand, the emission spectrum of MAPbX3 single crystals at low temperatures measured by photoluminescence (PL) spectroscopy consist of several PL bands  and the spectral overlap impedes precise extraction of spectral width and intensity.
Here we study the excitonic properties in MAPbI3 single crystals by means of simultaneous temperature-dependent photocurrent (PC) and PL measurements. The PL and PC data at low temperatures consistently show a sharp structure, providing conclusive evidence for the existence of free excitons in MAPbI3 single crystals. We find that the temperature-dependent PC spectral width reflects the scattering processes of the free excitons more correctly than the PL spectral width. The PC data reveal that the exciton–phonon couplings in orthorhombic-phase MAPbI3 are stronger than those in other conventional inorganic semiconductors. The longitudinal optical phonon energy is estimated to be 16.1 meV. By analyzing the temperature dependences of the PC and PL data with a simple model, we determined an exciton binding energy of 12.4 meV for MAPbI3 single crystals at low temperatures.
This work was partly supported by JST-CREST and JSPS-KAKENHI.
 (a) W. S. Yang et al., Science 348, 1234 (2015); (b) H. Zhu et al., Nat. Mater. 14, 636 (2015); (c) Q. Lin et al., Nat. Photon. 9, 687 (2014).
 (a) K. Tanaka et al., Solid State Commun. 127, 619 (2003); (b) L. Q. Phuong et al., J. Phys. Chem. Lett. 7, 2316 (2016).
 H.-H. Fang et al., Adv. Funct. Mater. 25, 2378 (2015).
9:00 PM - ES1.8.08
Photoluminescence Hysteresis in Organometal Halide Perovskite Solar Cells
Zhihua Xu 1 Show Abstract
1 , University of Minnesota, Duluth, Minnesota, United States
Electrical field modulated photoluminescence (PL) of organometal halide perovskite solar cells are investigated with the aim to gain deeper insight about the underlying mechanism of current-voltage (J-V) hysteresis. We observe PL intensity and lifetime of perovskite solar cells show significant hysteresis when changing the sweeping direction of electrical field. PL hysteresis is found to be dependent on device structure and excitation wavelength. PL hysteresis can be explained by ion migration under electrical field, which has been widely accounted for J-V hysteresis in peroskite solar cells. Our result suggests the mobile ions not only change the internal electrical field of solar cells, but also serve as quenching centers for photogenerated charge carriers in perovskite solar cells.
9:00 PM - ES1.8.09
Understanding How Nanoscale Variations in Halide Stoichiometry Determine Charge Collection in Mixed-Halide Hybrid Perovskite Solar Cells
Yanqi Luo 1 , Sigalit Aharon 2 , Michael Stuckelberger 3 , Ernesto Magana 1 , Barry Lai 4 , Mariana Bertoni 3 , Lioz Etgar 2 , David Fenning 1 Show Abstract
1 Nanoengineering, University of California, San Diego, La Jolla, California, United States, 2 Institute of Chemistry, Casali Center for Applied Chemistry, The Hebrew University of Jerusalem, Jerusalem Israel, 3 Defect Lab, School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona, United States, 4 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
The spatial distribution of absorber elemental makeup determines the local electronic properties of solar absorbers and ultimately device performance. Lead based organic-inorganic perovskite solar cells have become one of the most active research areas in the solar community within the past few years, mainly due to their flexible and tunable optoelectronic properties. However, the microscopic effects of A-site cation and halide substitution on carrier-charge transport have not been fully clarified in these mixed-chemistry systems. In this study, a nanoscale spatial variation of Br incorporation is found in both iodide rich and poor FAPbI3-xBrx solar cells by means of non-destructive synchrotron-based nanoprobe X-ray fluorescence (Nano-XRF). Simultaneous collection of spatially-resolved X-ray beam induced current (XBIC) maps reveal large variations in local photocurrent collection. The application of these characterization techniques to the mixed-halide perovskites allows us to precisely superimpose the halide heterogeneity on the corresponding photocurrent response with resolution down to 200 nm. Combining the local elemental information from Nano-XRF and the local optoelectronic response from XBIC reveals the electronic role of Br substitution and opens new directions toward understanding the tuning of mixed-cation and mixed-halide perovskite systems toward optimal device efficiency.
9:00 PM - ES1.8.10
First-Principles Design of New Electrode Materials in CH3NH3PbI3 Solar Cells
Wenmei Ming 1 , Dongwen Yang 2 , Lijun Zhang 2 , Mao-hua Du 1 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Jilin University, Changchun China
CH3NH3PbI3-based solar cells have shown remarkable progress in recent years but have also suffered from structural, electrical, and chemical instabilities and the resulting degradation. It was shown recently in CH3NH3PbI3 thin film solar cells that Au atoms from Au electrode can diffuse through hole transport layer and CH3NH3PbI3 layer at 70 °C, leading to significant degradation of the solar cell. We performed density functional theory calculations to study Au and Ag impurities in CH3NH3PbI3. The results show that the Au impurity on Pb site is a deep acceptor, which can cause deep hole trapping and nonradiative recombination, consistent with the observed solar cell degradation due to Au diffusion. On the other hand, Ag diffusion from the Ag electrode into the CH3NH3PbI3 layer may be prevented by the formation of AgI at the interface. We further studied formation and diffusion of many transition metal impurities (e.g., Ni, Co, Pd, Mo, W) in CH3NH3PbI3. Our results point to several new metal electrode materials for CH3NH3PbI3 solar cells. These metals have low resistivities as well as appropriate work functions for forming Ohmic contacts with CH3NH3PbI3 and the hole transport material. Importantly, they do not cause significant atomic diffusion from the electrode to the CH3NH3PbI3 layer (compared to Au) due to high formation energies and/or high diffusion barriers of the metallic impurities in CH3NH3PbI3.
9:00 PM - ES1.8.11
The Effect of Liq Layer on Inverted Perovskite Solar Cells—Working Mechanism & Stability Analysis
Hyunho Lee 1 , Kunsik An 1 , Seunghyun Rhee 1 , Priyanka Tyagi 1 2 , Changhee Lee 1 Show Abstract
1 , Seoul National University, Seoul Korea (the Republic of), 2 , University of Surrey, Guildford United Kingdom
The stability and reliability are still in big issue on the research field of perovskite solar cells. Perovskite film or materials are easily dissolved in polar solvents such as dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and, especially, water (H2O). This characteristic leads the easy fabrication of solution processed perovskite solar cells in room temperature, but causes many life time-related problems. Under certain humidity, water molecular permeate into the perovskite layer. The black-brown colored perovskite crystals slowly break down into the yellow phase which corresponds to lead iodide (PbI2). This phase transition causes high I-V hysteresis, low light response, decrease of absorption and short life time. To solve this problems, many groups focused on material development such as cesium iodide (CsI), lead bromide (PbBr2) and formamidinium iodide (FAI). However, the degradation sources of perovskite solar cells were not fully studied. In this work, we inserted different thickness of 8-hydroxyquinolatolithium (Liq) to the inverted perovskite solar cells as an electron extraction layer which is located between PCBM and Ag electrode. Liq layer inserted perovskite solar cells showed better JSC, FF and PCE (over 10%). Even, the life time was better for the certain thickness of Liq layer inserted perovskite solar cells. We performed scanning kelvin probe microscopy (SKPM) and conductive atomic force microscopy (CAFM) to verify the working mechanism of Liq layer to the perovskite solar cells. Time-resolved photoluminescence (TRPL) analysis shows the effect of trap passivation of Liq layer. And shelf life time (over 1000 hour) were taken for the different thickness of Liq inserted perovskite solar cells. Time of flight secondary ion mass spectrometry (TOF-SIMS), finally, shows the degradation sources of perovskite solar cells (iodine diffusion, lead diffusion and Ag penetration) and give us how Liq work on enhanced device stability.
9:00 PM - ES1.8.12
Interplay between Static vs Dynamic Disorder and Its Influence on Electronic Properties of Hybrid Perovskite Semiconductor CH3NH3PbI3
Dinesh Kabra 1 , Shivam Singh 1 , Cheng Li 2 , Fabian Panzer 3 , K. L. Narasimhan 1 , Tanaji Gujar 4 , Anna Koehler 3 , Mukundan Thelakkat 4 , Sven Huettner 2 Show Abstract
1 , IIT Bombay, Mumbai India, 2 Organic and Hybrid Electronics Group, University of Bayreuth, Bayreuth Germany, 3 Experimental Physics II, University of Bayreuth, Bayreuth Germany, 4 Applied Functional Polymers, University of Bayreuth, Bayreuth Germany
Metal halide perovskite semiconductors have become a potential candidate for optoelectronic device community  and efforts from academic and industries laboratories are underway for deployment, in particular for photovoltaic applications . Outside environment is different from laboratory condition and in-depth understanding of temperature dynamics of these emerging materials is very essential. In this talk, we show the interplay of structural dynamics to electronic states of perovskite semiconductors, for which temperature coefficient of bandgap is positive. The temperature dependence of the optical properties of methylammonium lead iodide (MAPbI3 = CH3NH3PbI3) from room temperature to 6K. In both, the tetragonal (T> 163K) and the orthorhombic (T<163K) phase of MAPbI3, the band gap (from both ab-sorption and photoluminescence (PL) measurements) de-creases with decrease in temperature - in contrast to what is normally seen for many inorganic semiconductors, like; Si, GaAs, GaN etc. We show that in the perovskites reported here, the temperature co-efficient of thermal expansion is large and accounts for the positive temperature coefficient of the band gap. A detailed analysis of the exciton linewidth allows to distinguish between static and dynamic disorder. The low energy tail of the exciton absorption is reminiscent of Urbach absorption. The Urbach energy is a measure of the disorder, which is modelled using thermal and static disorder for both the phases separately. The static disorder component, manifested in the exciton linewidth at low tem-perature is small. Above 60 K, thermal disorder increases the linewidth. Both these features are a measure of the high crystal quality and low disorder of the perovskite films even though they are produced from solution.
 “Quantitative Correlation of Perovskite Film Morphology to Light Emitting Diodes Efficiency Parameters” N. K. Kumawat, N. Jain, A. Dey, K. L. Narasmhan, D. Kabra Adv. Func. Mater (2016) (DOI: 10.1002/adfm.201603219)
 “On the uniqueness of ideality factor and voltage exponent of perovskite-based solar cells” S. Agarwal, M. Seetharaman, N. K Kumawat, A. S Subbiah, S. K Sarkar, D. Kabra, M. AG Namboothiry, P. R Nair J. Phys. Chem. Lett. Vol. 5, pp- 4115 (2014)
 “Effect of Thermal and Structural Disorder on the Electronic Structure of Hybrid Perovskite Semiconductor CH3NH3PbI3” S. Singh, C. Li, F. Panzer, K. L. Narasimhan, A. Graeser, T. P. Gujar, A. Köhler, M. Thelakkat, S. Huettner, and D. Kabra J. Phys. Chem. Lett. Vol. 7, pp- 3014 (2016)
9:00 PM - ES1.8.13
Textured Perovskite Cells
Joop van Deelen 1 , Marco Barink 1 Show Abstract
1 , TNO, Eindhoven Netherlands
Most research of texturisation of solar cells has been devoted to Si based cells. For perovskites, it was assumed that texturisation would not have much of an impact because of the relatively low refractive indexes lead to relatively low reflection as compared to the Si based cells. However, our optical modeling shows that a significant gain in perovskite (1.55 Ev) absorption from 84.6% to 93.5% for the wavelength range of 400 nm up to 800 nm. The largest gain in absorption is achieved between wavelengths of 700 nm and 800 nm. Because this is a range with a high photon density, the current density increases up to 10rel.%.
We have modeled a wide variety of height and periods of the texture and show generic trends in performance with texture. Moreover, by introducing a texture, the light is locally concentrated, depending on the texture configuration. This offers new cell architectures with optimized front and back contacts. Moreover, it can serve as a way of overcoming potential bottlenecks in large scale production, because an array of texture induced micro solar cells could reduce the material requirements. In turn, this could ease the demand of homogeneity in large scale coating processes.
9:00 PM - ES1.8.14
Structural Investigation of Hybrid Perovskite CH3NH3PbI3-xBrx Solid Solution
Frederike Lehmann 1 , Alexandra Franz 1 , Daniel Toebbens 1 , Susan Schorr 1 2 Show Abstract
1 , Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin Germany, 2 Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin Germany
In the last years hybrid perovskites became attractive as photovoltaic absorbers with power conversion efficiencies exceeding 20% . These materials offer a broad range of properties, for instance a tunable wide-bandgap which is directly related to their chemical composition.
Hybrid perovskites can be described as ABX3 compounds, in which A is the organic unit (methyl ammonium, MA, [CH3NH3]+), B the lead cation (Pb2+) and X3 a halide anion (X = I-, Br-, Cl-). The free rotation of the methyl ammonium molecule at higher temperatures results in an orientational disorder, giving rise to a large variety of different temperature dependent structural modifications. Furthermore the substitution of halides additionally influences the ordering in the crystal structure and makes structural determination challenging.
Structural investigations on the methyl ammonium lead triiodide (MAPbI3) perovskite have shown three temperature dependent structural modifications: at low temperatures (below 162.2 K) MAPbI3 crystallizes in an orthorhombic (Pnma) perovskite structure, in which the orientation of the organic molecule is fixed; between 162.2- and 327.4 K the structure is tetragonal (I4/mcm) and the number of disordered states of the methyl ammonium molecule is increased to 8 possible orientations . Above 327.4 K the system stabilizes in a cubic phase (Pm-3m) with complete orientational disorder of the molecule . MAPbBr3 in contrast shows a phase transition at 235 K from the cubic (Pm-3m) to the tetragonal (I4/mcm) Perovskite structure. At 150 K, a transition to an incommensurate phase occurs followed by further distortion to an orthorhombic (Pnma) structure at 148 K .
Our focus lies on the systematic study of hybrid perovskite solid solutions with different constituents (MAPbI3-xBrx) with regard to temperature and composition dependent phase transitions. Powder samples are analyzed by synchrotron X-ray diffraction (HZB, BESSY II, KMC-2) and neutron powder diffraction (HZB, BER II, E9). The data are treated by a Rietveld refinement for structural characterization. Within this we are able to determine the correct position of the organic molecule, and anisotropic displacement parameters as well as the influence of the degree of substitution. Furthermore we can estimate miscibility gaps and establish the temperature dependent phase diagram of the solid solution by means of direct determination of the phase transitions and structural disordering.
 NREL chart-best research-cell efficiencies; http://www.nrel.gov/ncpv/images/efficiency_chart.jpg
 Franz, A., Többens, D. M. and Schorr, S., Cryst. Res. Technol. 2016, 51, 534-540
 Baikie et al. J. Mater. Chem.A, 2013, 1, 5628
 Swainson et al. Physical Review B, 2015, 92, 100303(R)
9:00 PM - ES1.8.15
Crystallographic Texture Control in Hybrid Organic-Inorganic Perovskite Thin Films
Min Chen 1 , Yuanyuan Zhou 1 , Nitin Padture 1 Show Abstract
1 , Brown University, Providence, Rhode Island, United States
The control of grain orientations in hybrid organic-inorganic perovskite (HOIPs) thin films can play a significant role in further enhancement of the performance (efficiency, hysteresis, stability, etc.) of the resulting perovskite solar cells (PSCs). Here, we demonstrate an effective protocol for the modification of the chemical potentials of specific HOIP crystal facets, which allows us to control the HOIP crystallization behavior from their precursor phases and form HOIP thin films with engineered crystallographic texture. The mechanisms responsible for textured growth of HOIP thin films are elucidated using a suite of materials-characterization tools. Based on this approach, we further co-relate the properties/performance of HOIP thin films with their crystallographic textures at the nano-scale, micro-scale, and device-scale, which provides new directions in the design and development of high performance HOIP-based thin-film PSCs of the future.
9:00 PM - ES1.8.16
BaTiO3 Nanoparticles Embedded CH3NH3PbI3-xClx Perovskite Solar Cells with Enhanced Open-Circuit Voltage
Chaminda Hettiarachchi 1 , Nicholas Harris 2 , Pritish Mukherjee 1 , Sarath Witanachchi 1 Show Abstract
1 , University of South Florida, Tampa, Florida, United States, 2 College of Optics and Photonics, University of Central Florida, Orlando, Florida, United States
The aim of this research is to enhance charge collection in organo-metal lead halide perovskite absorber methyl ammonium lead iodide chloride (CH3NH3PbI3-xClx) by establishing a local internal field that can reduce electron-hole recombination resulting in increased open circuit voltage and device current. The intrinsic ferroelectricity in nanoparticles of Barium Titanate (BaTiO3 -BTO) embedded in the solar absorber can generate such an internal field. In this work we are exploring a hybrid structure of CH3NH3PbI3-xClx perovskite and ferroelectric BTO nanocomposite FTO/AZO/CH3NH3PbI3-xClx:BTO/Cu as a new type of photovoltaic device. A low-pressure spray deposition process that is scalable to large-scale manufacturing was used for the growth of the multilayer structure. Aluminum doped zinc oxide (AZO) nanoparticles were spray deposited on fluorine-doped tin oxide (FTO) as electron collection layer. The growth process of the solar absorber layer includes the nebulization of a mixture of PbI2 and CH3NH3Cl perovskite precursors and BTO nanoparticles dissolved in DMF, and injection of the aerosol into a low-pressure chamber and subsequent deposition on AZO. While high percentage of BTO in the film increases the carrier collection, it also leads to reduced carrier generation. The effect of the nanoparticle concentration on open-circuit voltage, short-circuit current, and the structural, optical, and electrical properties of CH3NH3PbI3-xClx absorber will be presented.
9:00 PM - ES1.8.17
Geometrically Designing Stable Dopant Environments in Perovskite Photovoltaics
Nicole Onishi 1 , Ka Yi Tsui 1 , Robert Berger 1 Show Abstract
1 , Western Washington University, Bellingham, Washington, United States
Focusing on case studies relevant to perovskite photovoltaics, the replacement of lead with germanium in CsPbCl3 and CsPbBr3, we develop a novel geometric approach to design optimal environments for perovskite dopants. We extend the sphere-packing arguments that motivate the Goldschmidt tolerance factor, the traditional sphere-packing metric used to assess perovskite stability, beyond ABX3 perovskite compounds to doped and strained perovskite superstructures. In doing so, we examine a variety of dopant environments, and use density functional theory (DFT)-computed total energies and phonon frequencies to assess their stability relative to competing phases and structural distortions. We find that 1) a germanium dopant atom can effectively be stabilized in perovskite photovoltaic materials when surrounded by appropriately-sized neighbors, 2) epitaxial strain can further enhance this stabilization, and 3) we can devise a generalized tolerance factor to capture these effects.
9:00 PM - ES1.8.18
Thin-Film ‘Metamorphosis’ Behavior in Hybrid Halide Perovskites for High-Performance Solar Cells
Yingxia Zong 1 , Yuanyuan Zhou 1 , Shuping Pang 2 , Nitin Padture 1 Show Abstract
1 , Brown University, Providence, Rhode Island, United States, 2 Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao China
Formation of hybrid organic-inorganic perovskite (HOIP) thin films with desirable compositions and morphologies is one of the major challenges in the development of solution-processed perovskite solar cells (PSCs). Here, we observed a thin-film ‘metamorphosis’ behavior induced by methylamine gas, which converts a rough, photo-inactive NH4PbI3 thin film to a smooth, high-performance MAPbI3 thin film within less than 5 seconds. In-depth characterization studies reveal that chemical reactions with morphology-transforming/-preserving in nature are involved. This unique chemical behavior can be extended to forming other HOIPs and the general guidelines will be discussed. This ‘metamorphosis’ approach represents a new direction in processing of HOIP thin films for high efficiency, stable solar cells and is likely playing an important role on the future PSC commercialization.
9:00 PM - ES1.8.19
Fundamental Mechanisms Leading to Nucleation and Growth in the Solution Processing of Hybrid Organic Inorganic Perovskites
Blaire Sorenson 1 , James Stevenson 1 , Angela Harper 2 , Paulette Clancy 1 Show Abstract
1 , Cornell University, Ithaca, New York, United States, 2 Physics, Wake Forest University, Winston-Salem, North Carolina, United States
Power conversion efficiencies of hybrid organic-inorganic perovskite (HOIP) solar cells now rival those of traditional silicon-based solar cells. Unlike silicon, HOIPs is they can be processed directly from solution, leading to low-cost and energy-efficient fabrication. While many studies have shown that the composition of these solutions ultimately affects the cell’s efficiency, the underlying physics governing the solution processing of these devices is poorly understood and under-investigated due to the overwhelming complexity of the system. Despite the importance of understanding this correlation between processing and performance, the choice of species and the processing “recipe” still remains largely determined by an experimental trial-and-error approach. We have performed accurate ab initio Density Functional Theory (DFT) calculations of important moieties in solution and identified the Mayer Bond Order (MBO) as a metric of complexation effectiveness in solutions containing the building blocks of lead halide salts. We provide clear evidence that the high bonding power and Lewis basicity, measured by the MBO, provides a computationally efficient and accurate way to determine solvent performance and screen currently unused experimental solvents for their effectiveness, hence precluding the need for experimental trial-and-error. We have also studied the reaction of perovskite building blocks in solution (organic chaperone cations, halide choice, etc.) to determine the mechanism of complexation that is a pre-requisite for perovskite formation. Using Nudged Elastic Band (NEB) calculations of quantum mechanically modeled systems, we have found that for each choice of halide (iodine, bromine, chlorine), organic cation, (methylammonium, formamidinium or the organic cation substitute cesium) and solvent, the minimum energy states correspond to different geometries for each combination of component species. We use these preferred orientations to determine the minimum energy path of the reaction mechanism in solution. Understanding the underlying mechanism of formation represents a critical step in scaling up the fabrication of HOIP solar cells.
9:00 PM - ES1.8.20
Laser Crystallization of Organic–Inorganic Hybrid Perovskite Solar Cells
Jisun Yoon 1 , Taewoo Jeon 1 , Joonwon Lim 1 , Kyung Eun Lee 1 , Hyeong Min Jin 1 , Sang Ouk Kim 1 Show Abstract
1 , Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
Organic–inorganic hybrid perovskites attract enormous research interest for next generation solar energy harvest. Synergistic crystalline structures comprising organic and inorganic components enable solution processing of perovskite films. A reliable crystallization method for perovskites, compatible with fast continuous process over large-area flexible substrates, is crucial for high performance solar cell production. Here, we present laser crystallization of hybrid perovskite solar cells using near-infrared (NIR) laser (λ = 1064 nm). Crystalline morphology of CH3NH3PbI3 (MAPbI3) perovskite films are widely controllable with laser irradiation condition while maintaining film uniformity. Photothermal heating effectively assisted by interfacial photoconversion layers is critical for phase transformation without beam damage of multilayered device structures. Notably, laser crystallization attains higher device performances than conventional thermal annealing. Fast laser crystallization with manufacture level scan rate (1 m min–1) demonstrates inverted-type perovskite solar cells with 11.3 and 8.0% efficiencies on typical glass and flexible polymer substrates, respectively, without rigorous device optimization.
9:00 PM - ES1.8.21
Interface Modification by Simple Organic Salts Improves Performance of Planar Perovskite Solar Cells
Raja Siram 1 , Jaykrushna Das 2 , Boris Rybtchinski 1 Show Abstract
1 , Weizmann Institute of Science, Rehovot Israel, 2 , Indian Institute of Technology, Mumbai India
Perovskite solar cells have recently become a focus of interest because they can potentially be fabricated as lightweight flexible coatings over large-area flexible substrates using low cost solution processing techniques. The high open circuit voltage (VOC) of a perovskite solar cell depends on the energy difference between work function of TiO2 and valence band of hole transporting layer (HTL). Recently, Ryu et al.,1 reported the VOC of 1.40 V by using methylammonium lead bromide (MAPbBr3) perovskite on mesoporous TiO2 scaffold with deep-highly occupied molecular orbital (HOMO) organic polymer, PIF8-TAA (HOMO=-5.51 eV) as HTL, whereas VOC of 1.29 V is obtained by Poly[bis(4-phenyl)(2,4,6-trimethylphenyl) amine] (PTAA) polymer, which has the HOMO of -5.14eV. In the latter case, maximum VOC of 1.29 V is observed which is contrary to the theory that VOC should not be exceeding the energy difference between work function of TiO2 and HOMO of PTAA. So, to study the role of HTL, we have fabricated perovskite solar cells with a simple organic salt used as HTL. The device architecture in our study is FTO/bl-TiO2/Mixed halide Perovskite/HTL/Au. MAPbBrxCl3-x Perovskite is deposited on bl-TiO2 layer by spin coating the solution of PbCl2 mixed with methylammonium bromide (MABr) in 1:3 ratio in DMF. Different concentrations of organic salt solution are deposited on the perovskite layer. The perovskite film is stable without diffusing the counter ions of salt into the perovskite layer which is confirmed by powder XRD. The valence band of the perovskite is calculated from the ultraviolet photoelectron spectroscopy (UPS) measurements. The fabricated devices are characterized by J-V measurements under illumination of AM1.5 and high power conversion efficiency (PCE) of 4.34% with VOC of 1.21 V, current density (JSC) of 6.32 mA/cm2, and fill factor (FF) of 57% have obtained. Without HTL, the characteristics are VOC=0.82 V, JSC=1.62 mA/cm2, and FF=48% with PCE=0.64. The external quantum efficiency (EQE) spectrum of devices with salt as HTL reveals almost 55% incident photon to current efficiency. These results indicate that a polar material that has a good charge transporting nature may act as HTL in methylammonium lead bromo chloride perovskite cells.
Ref:- 1. Ryu, S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Yang, W. S.; Seo, J.; Seok, S. Energy Environ. Sci., 2014, 7, 2614.
9:00 PM - ES1.8.22
Reflection-Absorption Infrared Spectroscopic Study of Perovskite Bulk and Interlayer Modification
Leo Hamerlynck 1 , James Stanfill 1 , R. Shallcross 1 , Neal Armstrong 1 Show Abstract
1 , University of Arizona, Tucson, Arizona, United States
We characterize the adsorption of self-assembled monolayers (SAMs) deposited on ultrathin (5-10nm) TiO2 on Au substrates and formation of solar-cell-relevant formamidinium lead perovskite (FAPbX3) films thereon using polarized Fourier transform reflection-absorption infrared spectroscopy (FT-RAIRS). Relative to traditional transmission FTIR experiments, FT-RAIRS probes the SAM/TiO2 interface with enhanced sensitivity, providing the means to characterize the binding and functionality of SAM-modified TiO2 substrates, which have shown the ability to significantly affect the morphology of the perovskite film.
In order to mitigate background signals in FT-RAIRS experiments, particularly for SAM interrogation, ultrathin and conformal TiO2 films are deposited on IR-reflective gold-on-glass substrates via chemical vapor deposition (CVD), which allows nanometer-scale control of the oxide thickness. SAMs with a variety of end-functional groups (e.g., -NH2, -Cl, -COOH, etc.) based on silane, carboxyl and catechol anchoring groups are adsorbed on top of the TiO2 layer via solution-phase methodologies. Methylammonium bromide (MABr)-doped formamidinium lead trihalide (FAPbX3) films are processed on control and SAM-modified TiO2 substrates using a DMSO-adduct approach, which affords high-quality perovskite films. In polarized FT-RAIRS, the surface selection rule dictates that only vibrational transitions with dipoles oriented normal to the Au surface plane may be detected due to selective use of p-polarized light; therefore, any changes in the RAIRS peak intensity ratios indicate orientation changes of the perovskite film that may result from interaction with the SAM-modified TiO2 substrate. These studies focus on experimental considerations related to formation of ultrathin TiO2 films using CVD, deposition of SAM films, characterization of perovskite vibrational peaks/peak ratios and determination of the interfacial phenomena that direct the properties of the bulk perovskite film.
9:00 PM - ES1.8.23
Correlating Microscale Luminescent and Photovoltaic Heterogeneity in Perovskite Solar Cells
Giles Eperon 1 , David Moerman 1 , David Ginger 1 Show Abstract
1 , University of Washington, Seattle, WA, United Kingdom
Whilst perovskite solar cells have demonstrated an unprecedentedly rapid rise in power conversion efficiencies to over 21%, they are still far off their theoretical maximums of >30%.1 Recently, several reports have emerged demonstrating that there is significant heterogeneity in the microscale properties of perovskite films – some grains seem to be of higher material quality than others, and grain boundaries show high densities of non-radiative defects.2,3 It has been suggested that this heterogeneity could limit the performance of solar cells made from these films. However, a direct link between film heterogeneity and device performance has not been shown.
Here, we probe heterogeneity on the microscale in full solar cell devices using a series of in-situ electrical and photophysical measurements, and show a direct link to solar cell performance for the first time. Using high-resolution spatially resolved luminescence mapping and laser beam induced current and voltage mapping, we find that there is significant variation in the photovoltaic performance of state-of-the-art perovskite solar cells across the device on the scale of microns. We correlate regions of high and low voltage and current (and hence PCE) with their luminescent efficiencies, and elucidate the impact that these regions have on photovoltaic performance.
We go on to show that certain passivation techniques can affect this device performance heterogeneity, with the most promising techniques showing fewer ‘dark’ grains and correspondingly higher photovoltaic performance. Based on our results we elucidate rational routes to pushing the performance of perovskite solar cells close to the thermodynamic limits.
(1) NREL. Best Research-Cell Efficiencies, http://www.nrel.gov/ncpv/images/efficiency_chart.jpg; 2016.
(2) Bischak, C. G.; Sanehira, E. M.; Precht, J. T.; Luther, J. M.; Ginsberg, N. S. Nano Lett. 2015, 150622162346003.
(3) de Quilettes, D. W.; Vorpahl, S. M.; Stranks, S. D.; Nagaoka, H.; Eperon, G. E.; Ziffer, M. E.; Snaith, H. J.; Ginger, D. S. Science (80-. ). 2015, 348 (6235), 683–686.
9:00 PM - ES1.8.24
Predicting the Morphology of Perovskite Thin Films via Crystal Growth Dynamic Studies of Sequential Deposition Method
Hyomin Ko 1 , Dong Hun Sin 1 , Min Kim 1 , Kilwon Cho 1 Show Abstract
1 , Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of)
We report the first detailed investigation of the kinetic analysis of the conversion process during the sequential deposition method (SDM), which is one of promising methods to high-quality organic-inorganic hybrid perovskite films. When applying the SDM, lead iodide (PbI2) is first deposited on a substrate to form closely packed PbI2 grains, and PbI2 is converted to perovskites (e.g. CH3NH3PbI3) by being dipped sequentially into organic solutions (e.g., CH3NH3I (MAI) in isopropyl alcohol (IPA)). Two reaction periods with different kinetics were identified. During the first period, perovskite crystals nucleated on the lead iodide surfaces and the reaction proceeded until the surface was completely converted to perovskites. The reaction during this period determined the surface morphology of the perovskites. A classical kinetic model, Johnson-Mehl-Avrami-Kolmogorov (JMAK) model which correlates the solid-solid phase transformation kinetics to the nucleation and growth processes can be applied to this process, and the overall reaction rate (r) is related to the average grain size R by . In this way, r was used to predict the surface morphology of the perovskite under certain processing conditions. Further conversion of residual PbI2 occurred during the second period. This conversion did not initially affect the surface morphology of perovskites; however, single-crystalline perovskite nanostructures (e.g., nanorods, nanoplates, nanorods) did form during the second period, so the surface morphology did change as the reaction time increased. The current study has furthered the understanding of detailed features of the SDM, enabled a reliable prediction of the final perovskite morphology resulting from specified processing conditions, and contributed to a reproducible fabrication of high-quality perovskite films.
9:00 PM - ES1.8.25
Enhanced Performance of Perovskite Solar Cells by Employing Plasmonic Au@SiO2 Core-Shell Nanoparticles
Siva Chandra Sekhar Pakanati 1 , Vamsi Krishna Komarala 1 , Qiquan Qiao 2 Show Abstract
1 Center for Energy Studies, Indian Institute of Technology, New Delhi India, 2 Electrical Engineering & Computers Science, South Dakota State University, Brookings, South Dakota, United States
Organic-inorganic hybrid metal halide (CH3NH3PbX3, X = Cl, Br and I) perovskite solar cells (PSCs) have gained an immense interest in the photovoltaic community due to their rapid improvement in power conversion efficiency (PCE), and further cost-effectiveness. Several strategies and fabrication techniques are employed to improve the morphology and electronic properties of perovskite thin films, and device structure to obtain high photovoltaic performance of PSCs. To further improve the PCE of PSCs, one of the methods is employing plasmonic metal nanoparticles (NPs) for enhancing an optical absorption in perovskite thin film without any changes in the perovskite layer and the device structure. Herein, we have demonstrated the plasmonic effect of Au@SiO2 core-shell nanoparticles (NPs) on the photovoltaic performance of PSCs comprising a device architecture of ITO/PEDOT: PSS/CH3NH3PbI3/PCBM/Rhodamine/Ag. In total, four batches of devices are fabricated by varying different concentrations of Au@SiO2 NPs ranging from 0 to 1.6 wt.% with an interval of 0.4 wt.%. The Au@SiO2 NPs were embedded at the interface between the PEDOT: PSS layer and the active perovskite layer. Characterization techniques like SEM, XRD, AFM, optical and electrical measurements have been conducted to study the effect of Au@SiO2 NPs on perovskite films as well as on device performance. We have noticed a minimal change on morphology and crystallinity of perovskite films, and found a significant improvement in a device performance, owing to the photocurrent enhancement from 17.86 mA/cm2 to 23.13 mA/cm2 and PCE improvement from 11.44% to 14.77%. The improvement in photovoltaic performance is attributed to the light harvesting efficiency (LHE) enhancement by the perovskite films under the influence of plasmonic Au@SiO2 NPs. The metal NPs acts as subwavelength antennas to couple an incident light into the perovskite layer, thereby enhancing the LHE and further an increase in the charge carrier generation. Some more experimental details and plasmonic device properties will be presented and discussed in the meeting.
9:00 PM - ES1.8.26
Impact on Optoelectronic Properties and Device Performance of Perovskite Devices Prepared via Annealing in MACl Vapor
Dhruba Khadka 1 , Yasuhiro Shirai 1 , Masatoshi Yanagida 1 , Kenjiro Miyano 1 Show Abstract
1 , National Institute of Material Science (NIMS), Tsukuba Japan
We present herein a low temperature solution approach to enhance PCE of perovskite solar cell. We found that the perovskite films annealed in the atmosphere containing MACl vapor exhibit significantly improved film quality with better crystallinity, grain morphology and optophysical properties which resulted in more efficient devices of the best efficiency ~15.1% with narrow distribution and improved stability compared to devices without MACl treatment. The analysis of optoelectronic characteristics of devices revealed the mitigation of defect states, reduced defect density, improvement in carrier profile and passivation of recombination activities which leads to better optoelectronic quality of perovskite thin film. These results consolidate that the perovskite device subsequent with annealing in ambient MACl vapor is a significant step forward toward viable PV devices. A study to gain the insight of the microscopic mechanism of the post deposition treatment is underway.
9:00 PM - ES1.8.27
Understanding the Role of Halide on the Formation of Mixed Halide and Performance in Lead Halide Solar Cells
Md Abdul Kuddus Sheikh 1 , Son Singh 1 , Daekyun Jeong 1 , Rahim Abdur 1 , Bhabani Sankar Swain 1 , Jaegab Lee 1 Show Abstract
1 School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of)
Organic-inorganic hybrid perovskite solar cell possesses excellent electronic, chemical, and optical properties that make them attractive for next generation solar cells. Lead iodide is a precursor material in the fabrication of highly efficient perovskite solar cells. Usually Lead iodide is used as a high- energy photon detector for gamma-rays and X-rays, due to its wide band gap. Lead iodide can be used as an active semiconducting materials for solar cell with suitable structure.
But the surface coverage of Lead iodide film on meso-TiO2 is not good enough to achieve good device characteristics. So combination of Lead chloride, Lead bromide with Lead iodide is a good way to overcome the poor surface coverage of Lead halide.
In this study, mixed lead halide films was investigated to reveal the effects of the experimental variables such as lead iodide, lead chloride and Lead bromide composition, post annealing temperature, post annealing time on the growth and morphology of Lead halide films. Lead halide films were fabricated via two-step solution deposition using different composition of PbI2, PbCl2 and PbBr2 in N, N-dimethylformamide (DMF) on to meso-TiO2 coated FTO glass. For device fabrication Spiro-OMeTAD/evaporated MoO3 was used as a hole transport layer (HTL). We observed that PbBr2 mixed with PbI2 shows good surface morphology with large grain Lead halide film. A device with the structure of FTO/c-TiO2/meso-TiO2/ Lead halide/Spiro-OMeTAD/Au using 0.5 M PbBr2 mixed with 1.0 M PbI2 solar cell shows power conversion efficiency (PCE) of 5.01 % and 4.86 % in forward scan and reverse scan respectively.
Yabing Qi, Okinawa Institute of Science and Technology
Wei Huang, Nanjing Tech University
Nam-Gyu Park, Sungkyunkwan University
Kai Zhu, National Renewable Energy Laboratory
Applied Physics Letters | AIP Publishing
The Journal of Physical Chemistry Letters | ACS Publications
National Renewable Energy Laboratory
Nature Energy | Springer Nature
Science Magazine| AAAS
Wiley VCH Verlag GmbH &
ES1.9: Structure, Pb-Free, New Materials, Low Dimensional and Transistor
Thursday AM, April 20, 2017
PCC North, 200 Level, Room 224 B
9:00 AM - ES1.9.01
Amino Acid Crosslinked 2D/3D Perovskite and Ion Exchange Induced 2D-3D Perovskite Conversion
Yixin Zhao 1 , Taiyang Zhang 1 , Ge Li 1 Show Abstract
1 , Shanghai Jiao Tong University, Shanghai China
Organometallic halide perovskites of both the 2D A2BX4 perovskites and 3D ABX3 perovskites have recently emerged as a novel class of light absorbing materials with great promise for solar conversion applications. The perovskite quantum dots are usually synthesized by solution chemistry and then fabricated into film for device application with some extra process. Here it is reported for the first time to in situ formation of a crosslinked 2D/3D NH3C4H9COO(CH3NH3)nPbnBr3n perovskite planar films with controllable quantum confine via bifunctional amino acid crosslinkage, which is comparable to the solution chemistry synthesized CH3NH3PbBr3 quantum dots. These atomic layer controllable perovskite films are facilely fabricated and tuned by addition of bi-functional 5-aminovaleric acid (Ava) of NH2C4H9COOH into regular (CH3NH3)PbBr3 (MAPbBr3) perovskite precursor solutions. Both the NH3 + and the COO− groups of the zwitterionic amino acid are proposed to crosslink the atomic layer MAPbBr3 units via Pb–COO bond and ion bond between NH3+ and [PbX6] unit. Since the 2D perovskite without space prefer to overlap each other to form an uniformed precursor films, a novel 2D HMA1-xFAxPbI3Cl perovskite (x=0.1-0.9) was designed, which can be fast transformed into 3D MA1-xFAxPbI3 perovskite by Cl-I and H-FA(MA) ion exchange. This 2D–3D perovskite conversion is a promising strategy for fabricating mixed-cation lead halide perovskites.
 Li, G.; Zhang, T.; Guo, N.; Xu, F.; Qian, X.; Zhao, Y., Ion-Exchange-Induced 2D–3D Conversion of HMA1−xFAxPbI3Cl Perovskite into a High-Quality MA1−xFAxPbI3 Perovskite. Angew. Chem. Int. Ed. 2016, 55 (43), 13460-13464.
 Zhang, T.; Xie, L.; Chen, L.; Guo, N.; Li, G.; Tian, Z.; Mao, B.; Zhao, Y., In-situ Fabrication of Highly Luminescent Bifunctional Amino Acid Crosslinked 2D/3D NH3C4H9COO-(CH3NH3PbBr3)n Perovskite Film. Adv. Func. Mater. 2016, in press
 Zhang, T.; Guo, N.; Li, G.; Qian, X.; Zhao, Y., A Controllable Fabrication of Grain Boundary PbI2 Nanoplates Passivated Lead Halide Perovskites for High Performance Solar Cells. Nano Energy 2016, 26, 50-56.
9:15 AM - ES1.9.02
Effect of Perovskite Precursor Solutions on Structure and Properties of PEDOT:PSS and Photovoltaic Performance of Planar Perovskite Solar Cells
Jianyong Ouyang 1 Show Abstract
1 , National University of Singapore, Singapore Singapore
The perovskite layer of planar peorvskite solar cells (PSCs) is usually prepared by coating a
solution of perovskite precursors, that is, PbI2, PbCl2 and methylammonium iodide (MAI), on poly(3,4-
ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS, Clevios P VP Al 4083). Here, the deposition
of the perovskite layer from its precursor solution saliently affects the electronic structure and properties
of PEDOT:PSS films and thus the photovoltaic performance of planar PSCs. The conductivity of
PEDOT:PSS is significantly enhanced from 10�3 to 101 S cm�1. The conductivity enhancement is not due
to the solvent but mainly MAI. Even more significant conductivity enhancement occurs for PEDOT:PSS
films after being coated with a dimethylformamide (DMF) solution of MAI, while pure DMF only slightly
increases the conductivity of PEDOT:PSS by a factor of 2–3. PEDOT:PSS films become rougher after the
deposition of a perovskite or MAI layer. The conductivity enhancements are attributed to the phase
segregation of PSSH chains from PEDOT:PSS and the conformational change of PEDOT chains. The
treatment of PEDOT:PSS with the organic solutions of MAI and solvents of perovskite precursor solutions
also affects the photovoltaic performance of the planar PSCs.
9:30 AM - *ES1.9.03
Enhancement of Efficiency for Sn-Perovskite Solar Cell from View Point of Hetero-Interface Structure
Shuzi Hayase 1 Show Abstract
1 , Kyushu Inst of Technology, Kitakyushu Japan
Hybrid perovskite solar cells (PVK solar cell) have attracted interest because of the high efficiency. In our simulation, maximum efficiency can be obtained by harvesting light from visible region up to 900nm, supposing that voltage loss is 0.4 V. However, absorption edge of MAPbI3 is 800nm. One of the expected candidates for the light absorber is PVK consisting of Sn, because Sn perovskite has light absorption up to 1200nm (1). However, the efficiency was not satisfactory. In this presentation, the low efficiency is explained from the view point of Sn perovskite crystal defect and the hetero-interfaces for the Sn-PVK solar cells. We have already reported that Ti-O-Pb bonding is formed at the interface between titania surface and Pb-PVK layer and passivates the surface traps of titania and decreases charge recombination. Because of this, Jsc increased with an increase in the Ti-O-Pb bond density (2-5). In the case of PVK consisting of Sn, it was found that Ti-O-Sn bonding is formed at the interface between tiania and Sn-PVK layer, and creates traps, resulting in increasing charge recombination. In order to decrease the Ti-O-Sn bond density on titania, efficiency increased from 4% to 8%. The interface of hole transport layer/PVK layer is discussed in the same way (6).
1. Y. Ogomi, et al., J. Phys. Chem. Lett. 2014, 5, 1004-1011; 2. S. Nakabayashi, et al., J. Photonics for Energy; 2015, 5, 057410; 3. Y. Ogomi, et al., J. Phys. Chem. C, 2014, 118, 16651-16659; 4. Q. Shen, et al., Phys. Chem. Chem. Phys. 2014, 19984-19992; 5. Y. Ogomi, et al., Chem. Phys. Chem. 2014, 15, 1062-1069; 6. H. Moriya, et al., ChemSusChem. In press (2016).
10:00 AM - *ES1.9.04
Development of New Materials for Highly Efficient Perovskite Solar Cells
Tingli Ma 1 2 Show Abstract
1 , Dalian University of Technology, Dalian China, 2 , Kyushu Institute of Technology, Kitakyushu, Fukuoka, Japan
Perovskite solar cells (PSCs) have attracted much attention due to their high-energy conversion efficiency and low production cost. However, the problems of stability and toxicity for PSCs are still unresolved. Our group carried out the studies on the PSCs from the fundamentals to their devices, including development of a series of materials for compact layer, active layer, hole transfer layer, as well as back electrodes.
Here, we present several kinds of inorganic ESLs based on amorphous WOx and its composite with NbOx, as well as SnO2 and WS2 for the PSCs. It is revealed that the composite of NbOx and WOx can improve the charge injection, transmission, and the donor density. The energy band structure and the depletion layer at the interface of ITO/ESL can also be modified. As a result, a 15.65% of PCE for the planar flexible PSC has been obtained based on the composite ESLs of NbOx and WOx fabricated at low temperature. Our recent results of Pb-free perovskites will also be presented.
 J. T.-W. Wang, J. M. Ball, E. M. Barea, A. Abate, J. A. Alexander-Webber, J. Huang, M. Saliba, I. Mora-Sero, J. Bisquert, H. J. Snaith, R. J. Nicholas, Nano Lett. 2014, 14, 724.
 K. Wang, Y. Shi, Q. Dong, Y. Li, S. Wang, X. Yu, M. Wu, T. Ma, J. Phys. Chem. Lett. 2015, 6, 755.
 K. Wang, Y. Shi, Y. Li, S. Wang, X. Yu, M. Wu, T. Ma, Adv. Mater 2016. 28, 1891–1897
10:30 AM - ES1.9.05
Selective Dissolution of Halide Perovskites as a Step towards Cost-Efficient Recycling Solar Cells
Donghoe Kim 1 , Byeong Jo Kim 2 , So Yeon Park 2 , Zhen Li 1 , Kai Zhu 1 , Hyun Suk Jung 2 Show Abstract
1 , National Renewable Energy Laboratory, Lakewood, Colorado, United States, 2 School of Advanced Materials Science & Engineering, Sungkyunkwan University, Suwon Korea (the Republic of)
The perovskite solar cells (PSCs), which had comparable photovoltaic (PV) performance (22.1 %) to that of other commercialized solar cells, such as c-Si (21.3%), CdTe (22.1%) and CIGS (22.3%) solar cells, need to address the several problems, such as reduction of unit price for fabrication of PV module, long-term stability, and phase stability. The recycling of degraded PV modules has been considered as an alternative approach to solve the cost reduction. Furthermore, considering the energy payback time (EPBT), which is the time required for a PV module to produce an amount of energy comparable to that consumed during its production, the EPBT of a perovskite PV module is 0.22 years, which is the shortest nominal EPBT compared with all other competitors such as c-Si and CdTe. Therefore, if it were possible to recycle degraded perovskite PV modules, the long-term stability issue inhibiting the commercialization of perovskite PV modules would be also solved. Therefore, in this paper, we introduce a recycling or repair methodology for PSCs. In this system, general mixed cation and mixed halide perovskite materials, such as CH3NH3PbI3 (MALI), HC(NH2)2PbI3 (FALI), and (FALI)0.85(MALBr)0.15, are removed through a selective dissolution process. This process is capable of dissolving PSCs such that the Au electrodes and the mp-TiO2-coated transparent conducting glass (TCG) substrates are separated through the dissolution of the perovskite layers. We find that the recycling of PSCs can be realized based on the removal of trihalide perovskite materials and that a small amount of Pb residue has a negligible effect on the ability to reuse the mp-TiO2-coated TCG substrate. The selective dissolution mechanism is attributable to the breaking down of the PbI6 octahedral frame in the trihalide perovskite owing to the reaction between the partially positive Pb2+ ions and a polar aprotic solvent. When the regenerated electron-transport-layer-coated FTO glass is reused, the original power-conversion efficiency is well retained over 10 regeneration cycles.
ES1.10: Structure, Materials Properties and Low Dimensional
Thursday PM, April 20, 2017
PCC North, 200 Level, Room 224 B
11:15 AM - *ES1.10.01
The Key Role of Materials Science in the Advancement of Halide-Perovskite Solar Cells
Nitin Padture 1 , Yuanyuan Zhou 1 Show Abstract
1 School of Engineering, Brown University, Providence, Rhode Island, United States
Halide perovskites (HPs) materials are at the heart of the emerging thin-film perovskite solar cells (PSCs) that are revolutionizing the field of photovoltaics. The advances in PSCs are being led by the synthesis/processing of high-quality HP thin films with engineered microstructures (e.g. grain morphology, grain boundary, defects, etc.). Here, we are using fundamental materials-science concepts including nucleation/growth, grain-coarsening, and self-assembly for the rational design of inherently-scalable approaches for forming HP thin films with precisely tailored microstructures. The fundamental mechanisms underlying these microstructural engineering approaches are elucidated via extensive materials characterization. Insights into the basic correlations between the engineered thin-film microstructures and the performance (efficiency, stability) of the PSCs fabricated from these films are presented. Based on these results, guidelines for the design of synthetic approaches and microstructures for next-generation high-performance, large-area PSCs are provided. The future challenges and opportunities are discussed in the context of how basic materials science can play a key role in the advancement of PSCs.
11:45 AM - *ES1.10.02
The Synthesis of Multi-Dimentional Perovksite Crystals and Device Fabrication
Huanping Zhou 1 Show Abstract
1 , Peking University, Beijing China
Organic inorganic hybrid perovskite with desired organic cations or halides has attracted increasing attention due to the excellent optoelectronic property. Here, we developed solvent-based synthetic methods for highly uniform multi-dimentional perovksite crystals, including 0D nanocrystals, 1D nanowires, 2D thin film, 3D single crystals, and studied the corresponding device performance. These work include: 1) The whole series of lead halide perovskite (APbX3, A=Cs, MA+, FA+; X=Cl-, Br-, I-) 0D nanocrystals (NCs) were successfully synthesized; 2) Millimeter-scale lead iodine-based perovskite 1D NWs employing various A-site substitutions, namely, Cs, MA+, and FA+, have been synthesized via a simple solvent-mediated intercalation process with nearly 100% yield; 3) The 2D perovksite film with large grains and low intrinsic defects level were obtained by tuning the coordination capability of additives in the precursors; 4) The 3D perovksite single crystals were synthesized by a modified inverse temperature crystallization method, where the structural and optoelectronic property was performed thoroughly. These results highlight the importance of precursor chemistry that governs the crystal quality of inorganic-organic halide perovskite, which will benefit further fundamental materials study and device performance.
12:15 PM - ES1.10.03
Metal to Halide Perovskite, HaP—A Novel Road to HaP Coating Directly from Pb(0) or Sn(0) Films
Yevgeny Rakita 1 , Nir Kedem 1 , Satyajit Gupta 1 , David Cahen 1 , Gary Hodes 1 Show Abstract
1 Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel
We will present a simple process to convert a metallic film of Pb(0), Sn(0) or a mixture of those to an ABX3 halide perovskite by introducing to AX [e.g., methylammonium iodide (MAI), MABr, CsI, etc.] salts dissolved in simple alcoholic solvents.(1) The novel approach allows a low toxicity process of forming a reproducible, high-quality, continuous films of various (including mixed) halide perovskites, that can be easily up-scaled to large areas. A much lower toxicity of this fabrication method is achieved by avoiding the use of polar aprotic solvents, such as dimethylformamide or dimethylsulfoxide, which are commonly used and become very toxic when containing Pb cations.
We will describe of our findings, including examples of the direct transformation from Pb or Sn to, for example, MAPbI3, MAPbBr3, MAPb(Br,I)3, FAPbI3, MASnI3 and the pseudo-perovskite Cs2SnI6. Apart from I-V characterizations of full devices, morphological and electro-optical characterizations will be presented.
(1) Y. Rakita, N. Kedem, D. Cahen, G. Hodes, Pat.Appl. # IL 245536 – ‘process for the preparation of halide perovskites and perovskite-related materilas’
12:30 PM - ES1.10.04
Understanding Film Formation Morphology and Orientation in High Member 2D Ruddlesden-Popper Perovskites for High-Efficiency Solar Cells
Chan Myae Myae Soe 1 2 , Wanyi Nie 2 , Konstantinos Stoumpos 1 , Hsinhan Tsai 2 , Jean-Christophe Blancon 2 , Fangze Liu 2 , Jacky Even 3 , Tobin Marks 1 , Aditya Mohite 2 , Mercouri Kanatzidis 1 Show Abstract
1 Department of Chemistry and Argonne-Northwestern Solar Energy Research Center, Northwestern University, Evanston, Illinois, United States, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 , Université Europeénne de Bretagne, Rennes France
Two-dimensional (2D) Ruddlesden-Popper (RP) perovskites have recently emerged as promising candidates for hybrid perovskite photovoltaic cells, realizing power-conversion-efficiency (PCE) over 10% with technologically relevant stability. To achieve solar cell performance comparable to state-of-the-art three-dimensional perovskite cells, it is highly desirable to increase the conductivity and lower the optical bandgap for enhanced near-IR region absorption by increasing the thickness of the 2D perovskite slabs. Here we report the use of the 2D higher member (n = 5) RP perovskite (n-butyl-NH3)2(MeNH3)4Pb5I16 in depositing vertically oriented thin films from dimethylformamide/dimethysulfoxide mixtures using the hot-casting method. These films are assembled into high-efficiency solar cells with an open circuit-voltage of ~1 V and PCE up to 10%. This is achieved by fine-tuning the solvent ratio, crystal growth orientation, and grain size in the thin films by employing our previously established hot-casting technique, coupled with solvent-engineering approaches. The enhanced performance of the optimized devices is ascribed to the growth of μm-sized grains as opposed to more typically obtained nm-grain-size and highly crystalline, densely-packed microstructures with the inorganic slabs preferentially aligned out of plane to the substrate, as confirmed by X-ray diffraction and grazing-incidence wide-angle X-ray diffraction mapping.
12:45 PM - ES1.10.05
Investigation on the Properties of Hybrid CH3NH3SnxI3 (0.9 ≤ x ≤ 1.4) Perovskite Systems
Lucangelo Dimesso 1 , Maximilian Stoehr 1 , Chittaranjan Das 1 , Thomas Mayer 1 , Wolfram Jaegermann 1 Show Abstract
1 , Technische Universitaet Darmstadt, Materials Science Dept., Darmstadt Germany
Alternatives to Pb in hybrid organic-inorganic methylammonium lead iodide (MAPbI3) perovskites for photovoltaic applications are necessary for their market acceptance due to the high toxicity and high recycling costs of Pb-containing materials. Sn-containing organic-inorganic perovskites are the most promising. In this work the investigation of the chemical and physical properties of Sn-containing perovskites as a function of the initial content of Sn is reported.
MASnxI3 (0.9 ≤ x ≤ 1.4) systems are prepared by self-organization process in aqueous solutions. X-ray diffraction analysis (XRD) of the “as prepared” MASnxI3 systems reveals the presence of CH3NH3SnI3 tetragonal phase (space group I4cm) and crystalline reflections of SnI2. The morphological analysis (by high resolution electron microscopy, HREM) shows the formation of irregular polyhedral crystallites (length between 50 – 400μm). After annealing in nitrogen at T = 150°C, t = 8h, the hybrid perovskites CH3NH3SnxI3 adopt cubic perovskite structure (space group P4mm) with crystallites of 2 – 4μm length. The optical investigations on the MASnxI3 systems show a dramatic dependence on the starting Sn-content with absorbance edges at 1107.0nm (x = 0.9), 1098.6nm (x = 1.0) and 1073.2nm (x = 1.1) respectively whereas at higher Sn-content (x ≥ 1.2) a broad tail of the absorbance profile has been observed.
The photoluminescence properties (PL) of the MA-Sn-I systems were investigated, in the wavelength range between 650nm and 1100nm, at room temperature using an excitation wavelength λexc = 500 nm. For x = 0.9 a band peaking at ≈1064nm has been detected whereas an additional band peaking at ≈1014nm has been observed at higher Sn-content (x ≥ 1.0). Moreover additional bands peaking at ≈1057nm, ≈1084nm respectively, with shoulders at ≈1035-1038nm and ≈1070nm, appeared by adding Sn2+ ions in the MASnI3 phase for 1.0 ≤ x ≤ 1.2. Finally, for x = 1.4 further additional bands peaking at ≈1040nm and ≈1068nm respectively have been detected. The origin and presence of more bands has been explained by supposing that the defect formation energy of Sn-vacancies generating hole is lower than those of any other defects, which means that Sn-vacancies is the most favorable intrinsic defect. This would indicate that a major p-type carrier source is Sn-vacancies and the black compound is a nearly intrinsic p-type semiconductor.
Films formation of MASnxI3 systems was demonstrated and closed layers were prepared by dissolving the annealed materials in N-N’-dimethylformammide (DMF), then by spin-coating in a glove-box under Ar-atmosphere. Similarly to the optical spectra, the J-V measurements revealed a semiconducting behavior of the devices at lower Sn-content (x ≤ 1.1).
This behavior was explained with the density of the Sn cation vacancies which are the most common defects in the Sn-containing systems and with the iodine stoichiometry in our annealed samples.
ES1.11: Traps, Device Stability, Electron and Hole Transport Layers
Thursday PM, April 20, 2017
PCC North, 200 Level, Room 224 B
2:30 PM - *ES1.11.01
Interaction between Halide Perovskite and Other Materials—A Chance to Tailor the Properties and to Boost Performance
Ivan Mora-Sero 1 Show Abstract
1 Institute of Advanced Materials, University Jaume I, Castelló de la Plana Spain
Halide Perovskite have certified efficiencies higher than 22%, with solution preparation methods. Solution methods allows the preparation at low temperature, and consequently halide perovskite can be fabricated without large and expensive facilities, and they can be easily combined with other materials. This fact opens a broad range of possibilities of material combination that can permit to increase halide perovskite solar cell performance and also tailor other properties as cell stability. In this presentation the interaction of perovskite with different materials are analyzed. First, we show that the substrate has an important effect on the properties of bulk perovskite. Later the modification of the surface interface by the addition of self assembly monolayers. Finally I will analyze the effect of combine organic molecules with perovskite, showing that these additives can enhance significantly cell performance. In addition, the interaction of perovskite with other materials, as PbS quantum dots, can produce interesting synergies able to use as the base of new and advanced optoelectronic devices.
3:00 PM - *ES1.11.02
Understanding Defect Physics in Metal-Halide Perovskites for Optimizing Optoelectronic Devices
Annamaria Petrozza 1 Show Abstract
1 Center for Nano Science and Technology at Polimi, Istituto Italiano di Tecnologia, Milano Italy
Semiconducting metal-halide perovskites present various types of chemical interactions which give them a characteristic fluctuating structure sensitive to the operating conditions of the device, to which they adjust. This makes the control of structure-properties relationship, especially at interfaces where the device realizes its function, the crucial step in order to control devices operation. In particular, given their simple processability at relatively low temperature, one can expect an intrinsic level of structural/chemical disorder of the semiconductor which results in the formation of defects.
Here I will review our understanding in the identification of key parameters which must be taken into consideration in order to evaluate the suscettibility of the perovkite crystals (2D and 3D) to the formation of defects, allowing one to proceed through a predictive synthetic procedure. I will discuss the role of defect physics in determing the open circuit voltage of metal halide perovskite solar cells and present technological strategies for the optimization of devices which include: 1) the engineering of the charge extracting layer (CEL), which accounts not only for the energy level alignment between the CELs and the perovskite, but also for the quality of the microstructure of the perovskite bulk film that is driven by the substrate surface; and 2) the use of inks based on colloidal suspensions of nanoparticles which lead to a high level of control over the material quality and device reliability, and offer more versatile processing routes by decoupling crystal growth from film formation.
3:30 PM - ES1.11.03
Probing Degradation in Perovskite Solar Cells and Progress towards Demonstrating Sufficient Stability
Rongrong Cheacharoen 1 , Duncan Harwood 2 , Colin Bailie 1 , Kevin Bush 1 , Axel Palmstrom 1 , Wen Ma 3 , Stacey Bent 1 , Michael McGehee 1 Show Abstract
1 , Stanford University, Stanford, California, United States, 2 , D2 Solar, San Jose, California, United States, 3 , Sunpreme, Sunnyvale, California, United States
Hybrid organic-inorganic halide perovskite solar cells have promising power conversion efficiencies above 20%. However, stability under standardized accelerated conditions has not been demonstrated. We improve stability of perovskite solar cells using three strategies. First, we replace the volatile methylammonium cation with cesium and formamidinium, which improves thermal stability and enables elevated temperature processing. We study the stability of 0.4cm2 active area single junction Cs0.17FA0.83Pb(Br0.17I0.83)3 perovskite employed in 24% efficient tandem solar cells. Second, we use an indium doped tin oxide (ITO) interlayer to prevent reaction between the metal electrode and the perovskite absorber. Moreover, the ITO acts as a barrier to prevent the diffusion of water in and components of the perovskite out at elevated temperatures. Third, we package the cells with glass front and back sheets, an encapsulant layer, and a butyl rubber edge seal to prevent the detrimental transport of molecules into and out of the perovskite solar cells.
We aged these packaged solar cells under multiple conditions according to the IEC 61646 thin film modules testing standard. After 1000 hours in the damp heat 85°C-85% humidity chamber, the packaged solar cells improved 20% in performance. Most of the improvement is due to an increase in Voc, which we hypothesize comes from the filling of shunt pathways at elevated temperatures. We decouple the effects of humidity from thermally induced degradation and find the acceleration factor as the packaged solar cells are aged at different elevated temperatures.
To determine mechanical stability of the packaged solar cells as the materials with different thermal expansion coefficients contract and expand throughout the day, we performed rapid temperature cycling between -40°C and 85°C. After two hundred temperature cycles, no delamination and a decrease in performance of less than 10% was observed for cells encapsulated in ethyl vinyl acetate. However, for cells encapsulated in Surlyn®, an ionomer resin, delamination and a corresponding drop in were observed after only one hundred cycles. We will discuss the quantitative difference in the mechanical robustness of packaged solar cells employing different encapsulants.
Under UV stress tests with both UVA and UVB, the Voc of the packaged solar cells increased more than 5% and overall performance was promising after 4 kWh/m2 UV exposure. Prolonged testing under UV exposure up to 15 kWh/m2 is ongoing and should elucidate the degradation pathway of packaged solar cells. Having passed many accelerated tests with glass on glass encapsulation, the stability of perovskite solar cells demonstrates great commercial promise.
3:45 PM - ES1.11.04
Trap-Limited Charge Transport in MAPbI3 Solar Cells with Tunability in Trap Concentration
Yuan Zhang 2 , Huiqiong Zhou 1 Show Abstract
2 School of Chemistry and Environment, Beihang University, Beijing China, 1 , National Center for Nanoscience & Technology, Beijing China
Solar cell performance, charge transport and relevant opto-electrical properties of solution processed methylammonium lead triiodide (MAPbI3) perovskites are comprehensively studied. Gains in the photocurrent are obtained by reducing the film thickness (L) of MAPbI3 solar cells traded off with by a reduction in the fill factor, leading to improved power conversion efficiencies over 11 % based on the planar device structure with simple Al cathode. With resort to a variety of experimental investigations, the carrier mobility of holes in MAPbI3 along the out-of-plain direction is determined to range between 10-2 to 10-3 cm2/Vs exhibiting an increasing trend with increasing L. The total trap density in MAPbI3 is in the order of 1015 to 1016 cm-3 with a trap energy around 64 meV. Consistently we observe trap-assisted charge recombination in MAPbI3 solar cells at different temperatures, irrespective of the perovskite layer thickness. The enhanced carrier mobility with the enlargement of L agrees with the reduction in trap densities determined by temperature dependent mobility measurements and photoluminescence decay dynamics the latter of which suggests the presence of longer-lived PL in thicker MAPbI3 films. The combination of these self-consistent results indicates that charge carrier mobility is not a dominating factor for the photocurrent losses in MAPbI3 solar cells with larger L while the traps indeed play a role for the solar cell parameters, which provide useful direction for further improvements. This work enables insightful understandings of the fundamental properties governing the device characteristics of solution-processed MAPbI3 solar cells.
ES1.12: Ion Migration, Phase Transition and Hysteresis
Thursday PM, April 20, 2017
PCC North, 200 Level, Room 224 B
4:30 PM - ES1.12.01
The Impact of Ion Migration on the Stability of Perovskite Solar Cells
Antonio Abate 1 Show Abstract
1 , Helmholtz-Zentrum, Berlin Germany
Perovskite solar cells are currently one of the most promising photovoltaic technologies for highly efficient and cost-effective energy production. In only a few years, an unprecedented progression of preparation procedures and material compositions delivered a prototype technology that exploits most of the potential for perovskites as photovoltaic materials. However, there still remains a huge scope to demonstrate that perovskite solar cells are stable under working conditions.
Migration of ions within the perovskite crystal lattice has been widely investigated to explain the “hysteresis” of current-voltage (J-V) characteristic of perovskite solar cells. The results of these studies indicated that regardless of the particular device architecture and materials composition, halides (and their vacancies) migrate within the perovskite layer and accumulate at the interface with charge selective contacts. Depending on particular voltage and light bias conditioning, accumulation of ions (and their vacancies) reduces the charge collection efficiency. This mechanism has been suggested as the most likely cause of J-V “hysteresis”, but it may also have a significant impact on the long-term stability of devices under working conditions. Understanding the impact of ion migration on device long-term performance is of paramount importance because it will answer the question whether or not there is an intrinsic instability that may ultimately prevent from using perovskites for photovoltaics.
In this talk, I will demonstrate ion migration in perovskite solar cells working under different voltage bias conditions and I will discuss the impact of ion migration on the initial device power conversion efficiency and long-term stability.
4:45 PM - ES1.12.02
Origin of Hysteresis in CH3NH3PbI3 Perovskite Materials
Ahreum Jeong 1 2 , Dasehee Seol 1 , Manhyung Han 1 , Seongrok Seo 2 , Tae Sup Yoo 3 , Woo Seok Choi 3 , Hyun Suk Jung 1 , Hyunjung Shin 2 , Yunseok Kim 1 Show Abstract
1 School of Advanced Materials Science and Engineering, Sungkyunkwan University (SKKU), Suwon Korea (the Republic of), 2 Department of Energy Science, Sungkyunkwan University (SKKU), Suwon Korea (the Republic of), 3 Department of Physics, Sungkyunkwan University (SKKU), Suwon Korea (the Republic of)
Organic and inorganic hybrid material of CH3NH3PbX3 with perovskite crystal structure have attracted considerable interest for high efficiency photovoltaic device applications due to high light absorption coefficient and low cost. However, achievement of higher efficiency has been impeded by hysteresis which can originate from a couple of different reasons such as ferroelectricity and ionic displacement. However, there is still lack of fundamental information on the origin of hysteresis in CH3NH3PbX3 perovskite materials. In this presentation, we explore origin of hysteresis in CH3NH3PbX3 perovskite thin films using atomic force microscopy (AFM). In particular, since main origins of the hysteresis are related to ferroelectricity and ionic displacement, we focus on the ferroelectric and ionic response on the various AFM modes with macroscopic voltage-current measurements. We found that, even though local response inside grains was primarily related to the ferroelectricity, global response including both grains and grain boundaries was related to the ionic displacement. This is because, whereas the grain boundaries degrades ferroelectricity, they can act as an ionic conducting path. The present results provide fundamental information regarding the origin of the hysteresis in the CH3NH3PbX3 perovskite materials and, further, could suggest insight on the material design for achieving higher efficiency.
5:00 PM - ES1.12.03
Understanding the Relationship between Ion Migration and the Anomalous Hysteresis in High-Efficiency Perovskite Solar Cells—A Fresh Perspective from Halide Substitution
Teng Zhang 1 , Haining Chen 1 , Yang Bai 1 , Shuang Xiao 1 , Shihe Yang 1 Show Abstract
1 , The Hong Kong University of Science and Technology, Hong Kong Hong Kong
Ion migration has recently piqued intensive attention with respect to the emerging perovskite solar cells (PSCs), but exactly how it impacts on cell performance is still elusive. In this paper, we validate a simple model to relate the scan rate-dependent hysteresis of the solar cells and the defect assisted ion migration in perovskite materials by means of halide substitution to form MAPbBrxI3-x (x~0–0.6), prepared by a modified two-step method so as to put the systematic study at a high solar cell efficiency level. Concurrent with the substantially increased power conversion efficiency (PCE), significantly reduced hysteresis has also been observed with increasing Br concentration. Bias-dependent kinetic measurements suggest that the hysteresis is caused by the redistribution of mobile ions (ion migration) under external bias and light illumination, which could be suppressed by Br substitution. Our Density Functional Theory study has borne out this notion by showing that the activation energy for I- (mobile species) migration has been increased from 0.34 eV in MAPbI3 to 0.46 eV in MAPbBrxI3-x. This work provides a new approach to fabricating hysteresis-free, high-efficiency PSCs and deepens our understanding of the hysteresis behavior in perovskite materials.
5:15 PM - ES1.12.04
Monitoring the Cubic-Tetragonal Phase Transition in Working CH3NH3PbI3 Solar Cells
Jeffrey Christians 1 , Laura Schelhas 2 , Joseph Berry 1 , Michael Toney 2 , Christopher Tassone 2 , Joseph Luther 1 , Kevin Stone 2 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States, 2 , SLAC National Accelerator Laboratory, Menlo Park, California, United States
The modest temperature of the tetragonal to cubic phase transition in CH3NH3PbI3 perovskite is likely to occur during real world operation of CH3NH3PbI3 solar cells. We monitor this phase transition by X-ray diffraction in a working perovskite solar cell simultaneously, or operando. This operando measurement is accomplished using a custom sample stage developed for simultaneous temperature-dependent current-voltage characterization of solar cells and X-ray diffraction. The tetragonal to cubic phase transition is observed in the working device to occur reversibly at temperatures between 60.5 and 65.4 °C, with some hysteresis in the transition temperature. By monitoring both structural phase and device performance in concert, we demonstrate that device performance remains consistent across this phase transition.
While typical materials exhibit discontinuities in optoelectronic properties across phase transitions, these results indicate a decoupling of device performance, and thus optoelectronic properties, from the change in the long range crystalline order across the phase transition. Refinement of the structural data acquired across this transition reveals significant anisotropic disorder on the iodine site of the cubic CH3NH3PbI3 lattice which is consistent with recent theoretical predictions of a highly dynamic crystal structure. Thus, the picture of cubic CH3NH3PbI3 which emerges is of a material which still appears locally tetragonal due to dynamic structural fluctuations even while it is globally changing from tetragonal to cubic. In addition, the methods developed for operando characterization of full, working device stacks is broadly useful for studying photovoltaic devices under a wide range of external stimuli.
5:30 PM - ES1.12.05
Acid Doping of Spiro-OMeTAD towards Planar Perovskite Solar Cells with High-Efficiency and Minimal Hysteresis
Zhen Li 1 , Jonathan Tinkham 2 , Philip Schulz 1 , Mengjin Yang 1 , Donghoe Kim 1 , Joseph Berry 1 , Alan Sellinger 1 2 3 , Kai Zhu 1 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States, 2 Department of Chemistry, Colorado School of Mines, Golden, Colorado, United States, 3 Material Science Program, Colorado School of Mines, Golden, Colorado, United States
Improving the electrical conductivity of hole transport materials (HTMs) is critical for achieving high-efficiency perovskite solar cells (PSCs). We demonstrated a new general doping strategy of spiro-OMeTAD, most commonly employed HTM in PSCs. Using acids of moderate strength is found to effectively enhance the hole transport properties of spiro-OMeTAD thin films. Unlike the common dopants Li-TFSI and/or Co(III) based salts, the acids do not induce an oxidative doping. Instead, the acids improve conductivity of spiro-OMeTAD through catalyzing oxidation and hydrogen bonding. The reported doping enhancement can be seen for a wide range of acids with different pKa and counter-ion identities (e.g. H2SO4, H3PO4 and acetic acid). Importantly, doping spiro-OMeTAD with acidic additives improves the overall PSCs performance, primarily through increase in open-circuit voltage and fill factor. Moreover, the device hysteresis is significantly suppressed with the acid additives. With the improved charge transport properties, we attain ~19% power conversion efficiency and hysteresis-free PSC in planar device geometry on TiO2 compact layer. The use of acidic additives represents a simple and general strategy to enhance charge transport properties of HTMs for developing high-efficiency and hysteresis-less PSCs.
5:45 PM - ES1.12.06
Deciphering Phase Transformation Induced by Ammonium Iodide in Perovskite Film Growth
Haonan Si 1 , Zhuo Kang 1 , Yue Zhang 1 Show Abstract
1 , University of Science and Technology Beijing, Beijing China
The past few years have witnessed the extraordinarily rapid development of a class of photovoltaic devices based on organometal halide perovskites. Nevertheless, so far such new-fangled materials still contain performance-limiting defects leading to a bad performance. Herein, we introduce a novel NH4PbI3-based intermediate phase in crystallization growth process. To control the nucleation and crystal growth process, NH4I additive is used to prepare perovskite films of high crystalline quality. A uniform and smooth perovskite film with reduced density of defects and long photoluminescence lifetime is obtained. The maximum power conversion efficiency of PSCs fabricated by this highly efficient film is up to 17%. The discovery of the innovative intermediate phase is probable to open a new sight to control crystallization of perovskite film and improve performance of PSCs.
ES1.13: Poster Session III
Friday AM, April 21, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ES1.13.01
Rationalizing the Light-Induced Phase Separation of Mixed Halide Organic-Inorganic Perovskites
Sergiu Draguta 3 , Onise Sharia 1 , Seok Joon Yoon 2 , Prashant Kamat 2 , William Schneider 1 , Masaru Kuno 3 Show Abstract
3 Department of Chemistry and Biochemistry, University of Notre Dame, South Bend, Indiana, United States, 1 Department of Chemical and Biomolecular Engineering, University of Notre Dame, South Bend, Indiana, United States, 2 Notre Dame Radiation Laboratory, University of Notre Dame, South Bend, Indiana, United States
Mixed halide hybrid perovskites, CH3NH3Pb(I1-xBrx)3, represent good candidates for low-cost, high efficiency photovoltaic and light-emitting devices. Their band gaps can be tuned from 1.6-2.3 eV, by changing the halide anion identity. Unfortunately, mixed halide perovskites undergo phase separation under illumination. This leads to iodine- and bromide-rich domains along with corresponding changes to the material’s optical/electrical response. Here, using combined spectroscopic measurements and theoretical modeling, we quantitatively rationalize all microscopic processes that occur during phase separation. Our model suggests that the driving force behind phase separation is the bandgap reduction of iodide-rich phases. It additionally explains observed non-linear intensity dependences as well as self-limited growth of iodide-rich domains. Most importantly, our model reveals that mixed halide perovskites can be stabilized against phase separation by deliberately engineering carrier diffusion lengths and injected carrier densities. This sets the stage for future studies which apply engineered mixed halide perovskites into optoelectronic applications.
9:00 PM - ES1.13.02
Electronic Structure and Polaronic Transport of Methylammonium Lead Bromide Crystals—Implications for Photo-Conversion Efficiency in Solar Cells
Hye Ri Jung 1 , Trang Nguyen 1 , Phuong Nguyen 1 , Gee Yeong Kim 1 , Seokhyun Yoon 1 , William Jo 1 , Won Seok Woo 2 , Chang Won Ahn 2 , Shinuk Cho 2 , Ill Won Kim 2 Show Abstract
1 Department of Physics, Ewha Womans University, Seoul Korea (the Republic of), 2 Department of Physics, University of Ulsan, Ulsan Korea (the Republic of)
Organic-inorganic lead halide based perovskite, CH3NH3Pb(Br,I)3, have risen to prominence with regards for their intimate physical properties. Most studies of all, examination on single crystals are proceeded to comprehend the intrinsic characteristics. Grain growth in perovksite is not fully controlled in terms of compositions, textures, and even believed as a trapping source of ionic migration. We investigate bromide perovskite single crystals for the distribution of surface electric potential and current transport by Kelvin probe force microscopy and conductive atomic force microscopy respectively. Surface potential exhibits distribution around 4.6 eV, which is a similar value with thin perovskite thin film. Current level of the mono-grain is smaller than thin films but some spots exhibit large current values at high external voltage bias. We also measured its photoluminescence and temperature dependent resistivity in order to estimate electronic structure and transport behaviors of the crystals.
9:00 PM - ES1.13.03
Preheating Assisted Deposition of Cesium Lead Halide Perovskite with Improved Efficiency for Solar Cells
Khan Mamun Reza 1 , Nirmal Adhikari 1 , Qiquan Qiao 1 Show Abstract
1 Electrical Engineering and Computer Science, South Dakota State University, Brookings, South Dakota, United States
In parallel to organic–inorganic lead trihalide perovskites, Inorganic Cesium based perovskite material are garnering interest due to thermal and humidity stability. Cesium Lead Bromide (CsPbBr3) is found to be highly stable in ambient environment, but the short circuit current is limited due to high band gap. In contrast, low band gap Cesium Lead Iodide (CsPbI3) is unstable in the black phase in ambient atmosphere and rapidly converts to non perovskite yellow phase. Mixed halide (CsPbBrI2) can be used to tune the band gap and also for higher stability at ambient environment. In this work, n-i-p structured perovskite solar cell made by single step method using CsPbBrI2 is demonstrated. Solubility limitations of the bromide ion were overcome by using both DMF and DMSO solvents. Different preheating temperatures were used before spin coating the perovskite film. The effects of the pre-heating temperature on film quality and device performance were studied. We found improved film quality and higher short circuit current with increasing the pre-heating temperature. Finally, the highest efficiency of 6.95% was obtained for sample preheated at 150 C.
9:00 PM - ES1.13.04
Relationships between Bulk Properties of CH3NH3PbI3-xClx Hybrid Lead Halide Perovskite Thin Films and Substrate—Beyond the Interface
Carmen Coya 1 , Esteban Climent-Pascual 2 , Jorge Moreno-Ramirez 1 , Angel Luis Alvarez 1 , Ivan Mora-Sero 3 , Alicia de Andres 4 Show Abstract
1 Escuela Técnica Superior de Ingeniería de Telecomunicación (ETSIT), Universidad Rey Juan Carlos, Madrid Spain, 2 Escuela Técnica Superior de Ingenieros Industriales, Universidad Politécnica, Madrid, Madrid, Spain, 3 Institute of Advanced Materials (INAM), Universitat Jaume I, Castellón Spain, 4 Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Científicas, Madrid Spain
Despite the enormous advances in terms of efficiency experienced in the last few years on halide perovskite solar cells, there are many aspects of these materials, as their photophysical properties and their relationship with structure and morphology, and of the devices constructed with them that are not completely understood. One important and controversial point, related with the working principles of perovskite devices, is the role of the selective contacts. Contacts affect charge separation and interfacial properties of perovskite devices, but there are many results that point to a deeper influence. For example, the hysteresis observed in operation conditions is tightly related to ion migration, which is a bulk property, and is also strongly dependent on the choice of contacts. The most accepted hypothesis attributes part of this hysteresis to bulk ion migration along the perovskite layer although this hysteresis is also strongly affected by the kind of substrate employed. In this work, films of CH3NH3PbI3-xClx are grown on electron and hole injection layers: compact TiO2, poly(3,4-polyethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), commercial fluorine doped SnO2(FTO) and bare glass for a comparative study. Along this talk we discuss how the substrate has an important effect on the bulk properties of the halide perovskite, not just in terms of crystalline grain size but also in terms of the chemical nature of the final perovskite layer, affecting the film defects, as our experiments points out. First we have determined with high precision, using synchrotron X-ray diffraction analysis, the cell parameters, preferred orientation and crystal size of halide perovskite films grown on different layers, observing a clear dependence of the parameters with the substrate, with 0.7 % variation in Pb-Pb distance. Second, we have analyzed the defect formation on this material by Raman analysis, distinguishing the degradation of the perovskite to lead oxide or lead iodine upon laser illumination in air. Increasing laser power lead to chemical transformation into PbOx identified by the 140 and 275 cm-1 Raman peaks, except for the layer on PEDOT:PSS. Third, we have intentionally degraded the samples by the use of increasing laser intensity and we have observed a different degradation behavior of the perovskite layer depending on the use of PEDOT substrate or oxide substrate. And forth, the results have been contrasted by a consistent analysis of photoluminescence evolution under continuous illumination. The Raman and PL experiments were done at room conditions. Our findings allow us to propose that the observed changes in the structure, crystal size and preferential orientation of the perovskite films as a function of the substrate are due mainly to the roughness of the surface but also to its chemical nature mainly by varying chlorine content and probably by the incorporation of oxygen and iodine vacancies during film nucleation and growth.
9:00 PM - ES1.13.05
Engineering Inorganic Lead-Free Perovskite CsSnI3—Materials Design, Theoretical Predictions and Efficient Photovoltaics
Ning Wang 1 2 , Yuanyuan Zhou 2 , Ming-Gang Ju 3 , Tao Ding 1 , Hector Garces 2 , Shuping Pang 4 , Xiao Cheng Zeng 3 , Nitin Padture 2 , Xiao Wei Sun 1 5 Show Abstract
1 , Nanyang Technological University, Singapore Singapore, 2 , Brown University, Providence, Rhode Island, United States, 3 , The University of Nebraska–Lincoln, Lincoln, Nebraska, United States, 4 , Qingdao Institute of Bioenergy and Bioprocess Technology, Qingdao China, 5 , Southern University of Science and Technology, Shen Zhen China
Perovskite solar cells (PSCs) based on hybrid organic-inorganic perovskites (HOIP) that contain lead have evoked widespread interest in both scientific and industrial communities. However, the use of lead-containing substances in electronic devices are severely restricted by many countries, motivating the development of lead-free PSCs. We demonstrate here the promise of emerging inorganic lead-free perovskite, cesium tin iodine (B-γ-CsSnI3), in thin-film PSCs, through materials design, theoretical predictions and efficient photovoltaics. The B-γ-CsSnI3 raw material was synthesized by melting it in evacuated tubes, and mixing it in a solvent consisting of a mixture of methoxyactonitrile dimethylformamide, and acetonitrile in 1:3:2 volumetric proportion was employed. By controlling the thermally-driven solid-state grain-coarsening B-γ-CsSnI3 microstructures were engineered. However, this is accompanied by an increase of tin-vacancy concentration in their crystal structures, as revealed by first-principle calculations and X-ray diffraction. Efficient planar heterojunction-depleted B-γ-CsSnI3 PSCs are achieved through optimization of the thin-film microstructures, combined with self-consistent device simulations. Furthermore, all-inorganic lead-free PSCs with high efficiency are also demonstrated. In addition, fluorine-substituted CsSnI3-xFx is considered, where density function theory calculations are used to elucidate the effect of fluorine on the crystal structure and electrical properties. High-performance CsSnI3-xFx PSCs were fabricated based on these predictions. The demonstrated strategies provide guidelines and prospects for developing future high-performance inorganic lead-free photovoltaics.
9:00 PM - ES1.13.06
High Open Circuit Voltages in Tin-Rich Low Bandgap Perovskites Based Planar Heterojunction Photovoltaics
Baodan Zhao 1 , Mojtaba Abdi-Jalebi 1 , Wanyi Nie 2 , Aditya Mohite 2 , Richard Friend 1 , Aditya Sadhanala 1 Show Abstract
1 , University of Cambridge, Cambridge United Kingdom, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Solution processable low bandgap perovskite semiconductors with a bandgap of ~1.1 eV have attracted lots of scientific interest as an alternative to silicon because of their capability to absorb a major portion of the solar spectrum reaching the surface of the earth. Recently, the anomalous bandgap changes in the lead and tin based binary metal CH3NH3(PbxSn1-x)I3 [ 0 ≤ x ≤ 1 ] perovskites have raised several interesting questions as to why they do not follow Vegards law. Here, we present a novel way of processing these perovskites that improves the morphology dramatically, leading to enhanced photophysical properties and device stability that is reflected in the substantial improvements observed in the solar cell performance based on these perovskites. Photovoltaic (PV) performance with power conversion efficiencies (PCEs) of ~ 10% is achieved in an inverted planar heterojunction architecture with negligible hysteresis for compositions with 60% and 80% Sn content and bandgaps of 1.27 and 1.19 eV, respectively. We attribute such high efficiencies to the small (< 450 meV) energy loss compared to the bandgap that implies a VOC operating close to thermodynamic limits, in addition to a very high (> 100 cm2V-1s-1) intrinsic carrier mobility. The observed improvement in device performance based on these low bandgap binary metal based perovskites opens up new possibilities of using these semiconductors for various optoelectronic applications.
9:00 PM - ES1.13.07
Improved Efficiency in CsSnI3-Based Pb-Free Perovskite Solar Cells via Grain Boundary Engineering
Srinivas Yadavalli 1 , Ning Wang 1 , Yuanyuan Zhou 1 , Nitin Padture 1 Show Abstract
1 School of Engineering, Brown University, Providence, Rhode Island, United States
The toxic nature of lead (Pb) in the state-of-the-art perovskite solar cells (PSCs) has been a major concern in the commercialization of this emerging photovoltaic (PV) technology. CsSnI3 is one of the most promising candidates to replace Pb-based perovskite material as absorber in PSCs. However, the reported efficiencies of CsSnI3-based PSCs are usually low, which can be due to the unbalanced carriers’ transport in the CsSnI3 thin films. Here, we demonstrate that carrier transport in solution-processed CsSnI3 thin films can be significantly improved by engineering CsSnI3 grain boundaries. The formation of desirable grain structures in CsSnI3 is confirmed through detailed materials characterization and spectroscopy. The effects of the engineered grain boundaries on the optoelectronic properties of CsSnI3 thin films is studied extensively. The use of this novel approach to achieve high performance in Pb-free PSCs lays down a promising path for the success of environmentally-friendly PSCs of the future.
9:00 PM - ES1.13.08
Interface Formation of Mixed Halide Perovskites and Its Influence on the Chemical and Electronic Structure
Evelyn Handick 1 , Golnaz Sadoughi 2 , Regan Wilks 1 3 , Leonard Koehler 1 , Claudia Hartmnann 1 , Thomas Kunze 1 , Roberto Felix Duarte 1 , Henry Snaith 2 , Marcus Baer 1 3 4 Show Abstract
1 Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin Germany, 2 Department of Physics, Clarendon Laboratory, University of Oxford, Oxford United Kingdom, 3 Energy Materials In-Situ Laboratory Berlin (EMIL), Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin Germany, 4 Institut für Physik und Chemie, Brandenburgische Technische Universität Cottbus-Senftenberg, Cottbus Germany
Recent records in conversion efficiency above 22%  demonstrate the high potential of hybrid organic-inorganic perovskite thin-film solar cells. The best efficiencies are being obtained by using mixed organometallic halide perovskites, ABX3 (A = MA, FA, Cs and/or Rb; B = Pb and/or Sn; and X = I, Br, and/or Cl). However, the fundamental properties of these material systems remain poorly understood. We have used non-destructive synchrotron-based hard x-ray photoelectron spectroscopy to study the interface formation of solution processed mixed methylammonium lead halide perovskites CH3NH3PbI3-xClx on compact and mesoporous TiO2 on FTO/glass substrates. By varying the CH3NH3PbI3-xClx layer thickness, we can monitor the chemical and electronic changes at this crucial interface between absorber and electron transport material (ETM).
We find that the chemical structure of the perovskite absorber changes with increasing layer thickness. Moreover, our study reveals how the ETM topography (i.e., of compact vs. mesoporous) impacts the interface formation and properties. The position of the valence band maximum (VBM) and the binding energy of the Pb 4f core level shifts with perovskite thickness indicating a pronounced interface induced band bending. In our presentation, we will – based on our data – deduce the absorber/ETM band alignment and discuss it against the performance of corresponding solar cell devices.
 http://www.nrel.gov/ncpv/images/efficiency_chart.jpg [accessed October 09, 2016]
9:00 PM - ES1.13.09
New Electron Transporting Material for Perovskite and Organic Hybrid Solar Cell
Pisist Kumnorkaew 1 , Khathawut Lohawet 1 Show Abstract
1 , National Nanotechnology Center, Klong Luang Thailand
We introduce a new electron transporting material (ETM) made of zinc cadmium sulfide and titanium oxides. This new material has shown significant enhancement in efficiency of photovoltaic devices such as Perovskite, Polymer, and Dye Sensitized Solar Cells. In this study, zinc cadmium sulfide suspension was added to titanium oxide sol-gel. The addition of zinc cadmium sulfide helps reduce energy level and increase electron transfer in electron transporting layer compared to that in the pristine titanium dioxide film. At the optimum addition of ZnCdS, at least 20 percent improvement of photovoltaic devices was observed. The mixture was prepared at room temperature and deposited to each type of solar cell via rapid convective deposition, in which only one-fifth of materials was consumed when compared with traditional spin coating technique. With the new ETM and convective deposition technique, high efficiency and low cost planar perovskite (> 13.5%PCE) or polymer solar cell (>7.5% PCE) can be fabricated.
9:00 PM - ES1.13.10
Dopant-Free Polymer HTM in Efficient and Stable Perovskite Solar Cell
Guan-Woo Kim 1 , Sung Yun Son 1 , Minjun Kim 1 , Gyeongho Kang 1 , Taiho Park 1 Show Abstract
1 , Pohang University of Science and Technology (POSTECH), Pohang, SE, Korea (the Republic of)
We report a dopant-free polymeric hole transport material (HTM) which is synthesized using benzo[1,2-b:4,5:b’]dithiophene and 2,1,3-benzothiadiazole and results in highly efficient and stable perovskite solar cells (~17.3% over 1400 h at 75% humidity). The HTM is composed of a random copolymer (RCP) which is the combination of BDT and DTBT and is characterized using UV–vis absorption spectroscopy, cyclic voltammetry, space-charge-limited current, and grazing-incidence wide-angle X-ray scattering. The perovskite solar cell employing RCP exhibits the highest efficiency (17.3%) in the absence of dopants [lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and tert-butylpyridine (tBP)]. The observed efficiency is ascribed to a deep HOMO energy level and high hole mobility. Besides, the water stability of the device is dramatically improved by avoiding deliquescent and hygroscopic dopants and by introducing the hydrophobic polymer layer. RCP devices maintain their initial efficiency over 1400 h at 75% humidity, whereas devices made from HTMs with additives fail after 900 h.
9:00 PM - ES1.13.12
Designing New Fullerene Derivatives as Electron Transporting Materials for Efficient Perovskite Solar Cells with Improved Moisture Resistance
Xiangyue Meng 1 2 , Shihe Yang 2 Show Abstract
1 , Beijing University of Chemical Technology, Beijing China, 2 , Hong Kong University of Science and Technology, Hong Kong Hong Kong
A new fullerene derivative named C5-NCMA is introduced as an electron transporting material (ETM) to replace the commonly used PCBM in the planar p-i-n perovskite solar cells (PVSCs). Compared with PCBM, this fullerene derivative features a higher hydrophobicity, higher LUMO energy level and higher ability of self-assembly. With the device structure of FTO/NiOx/MAPbI3/ETM/Ag, the C5-NCMA showed power conversion efficiency (PCE) of up to 17.6% with negligible hysteresis, which is higher than PCBM (16.1%). It was found that a higher LUMO energy level was obtained for C5-NCMA compared to PCBM, which favored a higher open-circuit voltage (Voc) in PVSCs with C5-NCMA than PCBM. Besides, the higher electron mobility, photoluminescence (PL) quenching efficiency and quenching rate of C5-NCMA led to more efficient electron transport and charge extraction in the device, thus resulting in a higher fill factor (0.79). Most importantly, the stability of PVSCs to moisture is significantly enhanced for C5-NCMA compared to PCBM due to the hydrophobic nature of C5-NCMA. Thus, we believe that the present work provides an important guide for the further development of ETMs for stable and efficient PVSCs.
9:00 PM - ES1.13.13
A Facile Molecularly Engineered Copper (II) Phthalocyanine as Hole Transport Materials for Planar Perovskite Solar Cells with Enhanced Performance and Stability
Guang Yang 1 , Hongwei Lei 1 , Cong Chen 1 , Xiaolu Zheng 1 , Junjie Ma 1 , Guojia Fang 1 Show Abstract
1 , Wuhan University, Wuhan, Hubei, China
Perovskite solar cells (PSCs) demonstrate huge potential in photovoltaic conversion, yet their practical applications face one major obstacle: their instability. As to conventional hole transport materials (HTMs) such as spiro-OMeTAD, their future commercialization maybe hampered for the cost and instability. Here, we report a new HTM of copper (II) phthalocyanine with octamethyl-substituted function groups (CuMe2Pc). Unlike the normal edge on orientation of pristine copper (II) phthalocyanine (CuPc), we found that CuMe2Pc could form face-on molecular alignment when deposited on perovskite via vacuum thermal evaporation, resulting in higher hole mobility, more condense thin film structure and more hydrophobic surface. These properties are more favorable for hole transport and moisture generated applications in PSCs. PSCs with planar structure were fabricated and tested, utilizing different phthalocyanines and spiro-OMeTAD as HTMs. PSCs with CuMe2Pc showed 25% higher power conversion efficiency (PCE) compared with those with CuPc. Furthermore, beneficial from the hydrophobic nature of CuMe2Pc, the devices with CuMe2Pc as HTM show improved stability and retained over 95% of their initial efficiencies even after storage in the humidity about 50% for 2000 h without encapsulation. This study demonstrates that CuMe2Pc is a potential HTM for fabricating low-cost and efficient PSCs with long-term stability.
9:00 PM - ES1.13.14
Improved Efficiency and Stability of Perovskite Solar Cells Employing a TiO2/ZnO Core-Shell Photoanode
Peng Chen 1 , Xingtian Yin 1 , Wenxiu Que 1 Show Abstract
1 , Electronic Materials Research Laboratory, Xi'an, Shaanxi, China
Since the pioneering work on introducing organometallic halide perovskite materials into dye-sensitized solar cells done by Miyasaka et al., perovskite solar cells (PSCs) have attracted extensive attention as the power conversion efficiency (PCE) boosts from preliminary 3.8% to 22.1% in early 2016. The electron selective contact plays a significant role in suppressing charge recombination and enhancing electron extraction, consequently in determining PSCs device final performance. Zinc oxide (ZnO) has been demonstrated to be a superb electron selective contact material in photovoltaic devices for its high electron mobility and various accessible nanostructures. However, issues of severe charge recombination and thermal instability occurring at the perovskites/ZnO interface hinder its application on perovskite solar cells. Herein, we report a strategy of TiO2 passivation onto the surface of ZnO nanorods (NRs) using a wet-chemical method, where a device structure FTO/ZnO NRs/TiO2 passivation layer/CH3NH3PbI3/spiro-OMeTAD/Ag is adopted. Based on the proposed strategy, an overall power conversion efficiency (PCE) of 13.49% is achieved mainly due to the improved open-circuit voltage (Voc) of 1.02 V, shirt-circuit current density (Jsc) of 20.69 mA/cm2, and fill factor (FF) of 0.64, which are much higher than those of bare ZnO NRs-based devices. Interestingly, TiO2 passivated samples show much better long-term device stability than those without passivation, where TiO2 acts as a buffer layer with improved thermal stability owning to reduced chemisorbed hydroxyl groups as indicated by X-ray photoelectron spectroscopy.
9:00 PM - ES1.13.15
Tuning the Energetics of Hole Transporting Materials for Perovskite Solar Cells by Alloying
Tracy Schloemer 1 , Jonathan Tinkham 1 , Dakoda Bradley 2 , Alan Sellinger 1 Show Abstract
1 Chemistry, Colorado School of Mines , Golden, Colorado, United States, 2 Chemistry, Reed College, Portland, Oregon, United States
Spiro-OMeTAD is currently the dominant hole transport material (HTM) in perovskite solar cells. However, it is labor intensive and costly to synthesize leading many research groups to develop more feasible alternatives. To this end, we have prepared an energetically tunable HTM system via alloying of different conjugated carbazole- and fluorene-cored HTMs to achieve desired EHOMO values. For example, we have prepared fluorinated hydrophobic conjugated carbazole HTMs with EHOMO levels below that of the perovskite valence band. However, an alloy system of spiro-OMeTAD and the fluorinated HTM showed a correlating increase in EHOMO as the blend ratio of spiro-OMeTAD increased. While this model system is promising, phase separation of blends is a concern after device integration. Thus we have also prepared cross-linkable alloyed HTMs in order to lock in the ideal structure and minimize any post-phase separation. These improvements will facilitate the integration of an alloying system to tune energetics of HTMs to better match the energetics of the perovskite, while maintaining morphology of HTM after device integration and use. In turn, this allows for maximization of Voc in devices alongside perovskite improvements that will make optimization of the device more efficient and drive down cost. This is collaborative work with the National Renewable Energy Laboratory (NREL).
9:00 PM - ES1.13.16
Cuprous Oxide Thin Films by Chemical Bath Deposition (CBD) for Perovkite Solar Cells
Odin Vallejo 1 Show Abstract
1 , IER-UNAM, Temixco, Morelos Mexico
Cuprous oxide (Cu2O) is a p type semiconductor with a direct band gap of about 2.17 eV. Due to its outstanding photoelectronic properties, natural abundance, non-toxic nature, and simple preparation procedures, Cu2O has generated interest in various applications, such as the conversion of solar energy into electrical or chemical energy, photochemical decomposition of water into O2 and H2 under visible-light irradiation, and because of its low electron affinity (3.2 eV) and very high hole mobility (256 cm2 V-1 s -1), this semiconductor has been suggested as a potential hole transporting material for Perovskite solar cells, in substitution of expensive 2, 2’, 7, 7’ tetrakis(N,N-di-p-meth oxyphenylamine)-9’,9-spirobifluorene (spiro-OMETAD). Hossain et al have simulated different hole transporting materials (HTM) for Perovskite solar cells including spiro-OMETAD, finding Cu2O as the most promising HTM.
We report an easy and direct CBD method for Cu2O thin films. These thin films have been treated by annealing and chemical solution treatments to improve its electrical properties. We have studied the effect of time deposition, pH, reactant concentration, stoichiometry, bath temperature and postdeposition annealing (Temperature and gas enviroment) and chemical solution treatments. The thin films were analyzed by X-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectroscopy (EDS), UV- vis spectroscopy and electrically characterized. The high hole mobility makes Cu2O thin films suitable for Pervoskite solar cells.
1.- Hossain, M. I., Alharbi, F. H., & Tabet, N. (2015). Copper oxide as inorganic hole transport material for lead halide perovskite based solar cells. Solar Energy, 120, 370-380.
2.- 2.- Xu, H. Y., Chen, C., Xu, L., & Dong, J. K. (2013). Direct growth and shape control of Cu 2 O film via one-step chemical bath deposition. Thin Solid Films, 527, 76-80.
9:00 PM - ES1.13.17
The Role of Polar Insulating Polymer in ZnO:Poly(Ethylene Glycol) Hybrid Interlayer for Highly Stable Perovskite Solar Cells
Dong Hun Sin 1 , Hyomin Ko 1 , Kilwon Cho 1 Show Abstract
1 , Pohang University of Science and Technology (POSTECH), Pohang-si Korea (the Republic of)
Methylammonium lead iodide (CH3NH3PbI3) perovskite layer is thermally unstable on bare ZnO layer because methylammonium ion is readily deprotonated with oxygen defects on ZnO surface. We first introduced a polar insulating polymer, poly(ethylene glycol) (PEG), into ZnO nanoparticle (NP) layer in order to passivate the oxygen defects on ZnO NPs. With the PEG hybridization, the CH3NH3PbI3 layer became mechanically adhesive and thermally stable on the ZnO:PEG layer because PEG increased the work of adhesion between the CH3NH3PbI3 and ZnO:PEG layer and prevented direct contact between the CH3NH3PbI3 layer and oxygen defects on ZnO NPs. We also systematically tailored the energy level of the ZnO layer by controlling the PEG content, which reduced the conduction band of the ZnO layer to be matched with the conduction band of the CH3NH3PbI3 layer; An electron-selective cathodic interface is formed with the energy level alignment for electron transfer and deep-lying valence band of ZnO for hole blocking from the CH3NH3PbI3 layer. As a result of stable and electron-selective interface, a power conversion efficiency recorded 15.5% with reduced charge carrier recombination loss and maintained over 1 year in a glove-box. We concluded that incorporating a polar insulating polymer into ZnO NPs is a powerful strategy for improving ZnO/CH3NH3PbI3 electron injection and interface stability, and the overall photovoltaic parameters of the perovskite solar cells.
9:00 PM - ES1.13.18
Highly Thin and Uniform Copper Thiocyanate Hole Transporting Layer for High Efficiency and Remarkable Long-Term Stability Perovskite Solar Cell by Spray Deposition
Inseok Yang 1 , Kiwoo Jung 1 , Wan In Lee 1 Show Abstract
1 Department of Chemistry and Chemical Engineering, Inha University, Incheon Korea (the Republic of)
Low cost coppoer based inorganic hole transporting material (HTM) which copper thiocyanate employing lead halide perovskite solar cells (PSCs) was developed by spray deposition in this work with high efficiency and outstanding long-term stability. We developed a reproducible method to deposit CuSCN layer on the CH3NH3PbI3 layer by a simple spray deposition technique, which does not appreciably damage the underlying CH3NH3PbI3 layer. The fabricated PSC with ~50 nm-thick pristine CuSCN layer (PSC-I) exhibited the photovoltaic conversion efficiency (PCE) of 17.10% with JSC of 23.10 mA/cm2, VOC of 1,013 mV and FF of 0.731. Comparing to the PSC employing spiro-OMETAD, its JSC is comparetively higher, suggesting that CuSCN is superior to spiro-OMETAD in transporting the holes, although its VOC is appreciably lower presumably due to the absence of additives in the CuSCN-based HTM. Furthermore, PSCs employing the pristine CuSCN demonstrate a remarkable long-term stability at ambient condition: PCE was decreased by only 5.8% after 100 days.
9:00 PM - ES1.13.19
Integration of <001> Oriented Anatase TiO2 Electron Transport Layer into Perovskite Solar Cells to Improve Carrier Separation
Hasti Gheibi Dehnashi 1 , Megan Mayer 1 , Alexander Yore 1 , Yen Tran 1 , Michelle Howard 1 , Akm Newaz 1 , Andrew Ichimura 1 Show Abstract
1 , San Francisco State University, San Francisco, California, United States
Since 2009, much progress has been made in perovskite solar cells. The perovskite light absorber methylammonium lead iodide (MAPbI3), can be made from inexpensive precursors, effectively separates charge carriers, and leads to devices with power-conversion efficiencies greater than 16%. In this work, we focus on the integration of <001> oriented anatase TiO2 films into the solar cell heterostructure. Titanium dioxide is a key component of the solar cell that serves as blocking and electron transport layers (ETL). The typical ETL is composed of amorphous or randomly oriented nanocrystalline TiO2. However, oriented thin films should improve charge carrier separation and collection. To construct our solar cells we spin-coat MAPbI3 onto <001> oriented anatase TiO2 thin films. The hole transport layer (HTL), spiro-OMeTAD, is deposited onto the MAPbI3 layer. We have studied the effectiveness of charge transport to TiO2 and the HTM by photoluminescence (PL) spectroscopy. It was observed that PL intensity of perovskite—TiO2 heterojunction decreases by 54% when TiO2 is annealed under H2 compared to MAPbI3 without an ETL. The PL intensity is further decreased in the presence of the HTM. The Bragg diffraction pattern of the perovskite thin film suggests that the MAPbI3 exhibits preferred orientation in the presence of <001> textured TiO2 which may improve carrier separation and overall device efficiency. The MAPbI3 prepared by a 2-step deposition method was compared to pre-made perovskite and found to have better stability in ambient air. Since grain size and orientation of CH3NH3PbI3 play an important role in the effectiveness of a solar cell, future work will involve fine tuning the deposition of perovskite in order to create efficient solar cells.
9:00 PM - ES1.13.20
Development of Semi-Transparent Perovskite Solar Cells for Tandem Applications
Yasuhiro Shirai 1 , Masatoshi Yanagida 1 , Takeshi Noda 1 , Liyuan Han 1 , Kenjiro Miyano 1 Show Abstract
1 , NIMS, Tsukuba Japan
Perovskite PV materials are unique polycrystalline semiconductors that can be deposited on surfaces using low-temperature solution-processes and achieve impressive high solar-to-electricity conversion efficiencies. It is also possible to tune the bandgap of the perovskite absorbers, especially for the hybrid organic lead trihalide perovskites, by controlling the halide (Cl, Br, and I) and organic (MAI, FAI, etc.) contents in the crystal. These features make it one of the best material for the top layer of tandem PV applications. To realize highly efficient and cost effective tandem PV devices, we have developed perovskite PV cells that is semi-transparent to the narrow bandgap absorbers such as single crystalline silicon (c-Si) having bandgap around 1.1 eV. We have tuned the bandgap of perovskite absorbers between 1.6 and 1.8 eV to match the bandgap of c-Si cells, and made the entire cell semi-transparent to the bottom c-Si cell by using the ITO electrodes for both top and bottom sides of the perovskite PV cells having the layer structure of ITO/ HTL/ Perovskite/ PCBM/ ETL/ ITO (HTL: hole transport layer, ETL: electron transport layer). The semi-transparent cells achieved over 13% efficiencies with the bandgap around 1.6 eV, whereas usual non-transparent devices with Ag electrode and the bandgap of 1.6 eV achieved over 18% efficiencies and that with 1.7 eV achieved over 15% efficiencies, through the effective combination of the HTL and ETL layer materials.
9:00 PM - ES1.13.21
Effect of Mixed Lead Halide Based Perovskite Films on Performance of Photodetectors
Son Singh 1 , Md Abdul Kuddus Sheikh 1 , Daekyun Jeong 1 , Rahim Abdur 1 , Jaegab Lee 1 Show Abstract
1 School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of)
Methyl Ammonium Lead Halide based perovskites are excellent new materials with high carrier mobility, high photo conversion efficiency and tunable bandgap. For these reasons it becomes one of the attractive light harvesting semiconducting materials. In addition, these materials have advantage of low temperature and easy processing, and facile scale-up. Furthermore, the perovskite materials are sensitive to a wide band wavelength from ultraviolet to visible range. However, the mechanism for the growth of the hybrid perovskite crystalline structure is not properly understood on the planar surfaces.
In this study, we have fabricated perovskite-based photodiode consisting of ITO/CdS/perovskite/V2O5/Au, focusing on the conformal coating of perovskite on the planar CdS by modifying the chemistry of perovskite. The addition of PbBr2 and PbCl2 to PbI2 significantly increases the nucleation rate of perovskite on CdS, leading to highly smooth surface morphology of perovskite and the resulting high performance of photodetectors. For example, the addition of chloride and bromide reduces the leakage current, and enhances the on-current and responsivity. We found that photodetector based on perovskite with molar ratio of 5:3:2 (PbI2:PbCl2:PbBr2) showed large detectivity and high EQE (80%). Systematic study of the effects of the composition of lead halides on the nucleation and growth of perovskite, its morphology, the performance of the photodetectors will be presented.
9:00 PM - ES1.13.22
Photo Detection Applications of Methyl Ammonium Lead Iodide Thin Films by Pulsed Laser Deposition
Nagabhushan Patel 1 , Sandra Dias 1 , S.B. Krupanidhi 1 Show Abstract
1 , Indian Institute of Science, Bangalore, KA, India
Organic-inorganic hybrid perovskite materials are considered as promising candidates for emerging thin-film photodetectors. In this work we discussed the application of the CH3NH3PbI3 thin films by pulsed laser deposition for photo detection applications. With this method we obtained high perovskite film coverage on FTO substrate and observed well formed grains. The films did not show any sign of degradation over months together.
We investigated the surface morphology and surface roughness of the films by field emission scanning electron microscope and atomic force microscope. We studied the optical responses of the films. Photoluminescence (PL) spectra was observed for all films which were grown at different deposition and annealing time durations, and the PL peak was found at 1.61 eV, 1.61eV, 1.6 eV and 1.62 eV respectively. Also, UV-Visible spectra has been observed for all the samples and band gap was found at 1.55 eV, 1.52 eV, 1.57 eV and 1.6 eV respectively. We also studied time resolved PL spectrum for all the samples and found that the decay time constant was increasing with time.
We carried out a study on solar and infrared photodetection using CH3NH3PbI3 thin films. The values of the responsivity, sensitivity, external quantum efficiency and specific detectivity under 1 sun illumination and 0.7 V bias were 105.4 A/W, 1.9, 238% and 1.5 × 1012 Jones respectively.
Yabing Qi, Okinawa Institute of Science and Technology
Wei Huang, Nanjing Tech University
Nam-Gyu Park, Sungkyunkwan University
Kai Zhu, National Renewable Energy Laboratory
Applied Physics Letters | AIP Publishing
The Journal of Physical Chemistry Letters | ACS Publications
National Renewable Energy Laboratory
Nature Energy | Springer Nature
Science Magazine| AAAS
Wiley VCH Verlag GmbH &
ES1.14: Synthesis, Scale-up Inks and Vapor-Based
Friday AM, April 21, 2017
PCC North, 200 Level, Room 224 B
9:00 AM - ES1.14.01
Improving the Performance of Formamidinium and Cesium Lead Triiodide Perovskite Solar Cells Using Lead Thiocyanate Additives
Yue Yu 1 , Changlei Wang 1 , Corey R. Grice 1 , Niraj Shrestha 1 , Jing Chen 2 , Dewei Zhao 1 , Weiqiang Liao 1 , Alexander J. Cimaroli 1 , Paul Roland 1 , Randy Ellingson 1 , Yanfa Yan 1 Show Abstract
1 , University of Toledo, Toledo, Ohio, United States, 2 , Southeast University, Nanjing China
Formamidinium lead triiodide (FAPbI3) is considered as an alternative to methylammonium lead triiodide (MAPbI3) due to its lower band gap and better thermal stability. However, due to the large size of FA cations, it is difficult to synthesize high quality FAPbI3 thin films without the formation of undesirable yellow phase. Smaller sized cations, such as MA and Cs, have been successfully used to suppress the formation of the yellow phase. While FA and MA lead triiodide perovskite solar cells (PVSCs) have achieved power conversion efficiencies (PCEs) higher than 20 %[3, 4], the PCEs of formamidinium and cesium lead triiodide (FA1-xCsxPbI3) PVSCs have only been around 16.5 %[2, 5-7]. Here, we report our examination of the main factors limiting the PCEs of (FA1-xCsxPbI3) PVSCs. We find that one of the main limiting factors could be the small grain sizes (around 120 nm), which leads to relatively short carrier lifetimes. We further find that adding a small amount of lead thiocyanate (Pb(SCN)2) to the precursors can enlarge the grain size of (FA1-xCsxPbI3) perovskite thin films and significantly increase carrier lifetimes. As a result, we are able to fabricate (FA1-xCsxPbI3) PVSCs with significantly improved open-circuit voltages (Voc's) and fill factors (FFs), and therefore enhanced PCEs. With an optimal 0.5 mol % Pb(SCN)2 additive, the average PCE is improved from 16.18 ± 0.50 (13.45 ± 0.78) % to 18.16 ± 0.54 (16.86 ± 0.63) % for planar FA0.8Cs0.2PbI3 PVSCs when measured under reverse (forward) voltage scans. The champion cell registers a PCE of 19.57 (18.12) % when measured under a reverse (forward) voltage scan, comparable with that of the best performing MA containing planar FA-based lead halide PVSCs.
 J.-W. Lee, D.-J. Seol, A.-N. Cho, N.-G. Park, Advanced Materials 2014, 26, 4991-4998.
 Z. Li, M. Yang, J.-S. Park, S.-H. Wei, J. J. Berry, K. Zhu, Chemistry of Materials 2016, 28, 284-292.
 W. S. Yang, J. H. Noh, N. J. Jeon, Y. C. Kim, S. Ryu, J. Seo, S. I. Seok, Science 2015, 348, 1234-1237.
 M. Saliba, S. Orlandi, T. Matsui, S. Aghazada, M. Cavazzini, J.-P. Correa-Baena, P. Gao, R. Scopelliti, E. Mosconi, K.-H. Dahmen, Nature Energy 2016, 1, 15017.
 J.-W. Lee, D.-H. Kim, H.-S. Kim, S.-W. Seo, S. M. Cho, N.-G. Park, Advanced Energy Materials 2015, 5.
 S. Wozny, M. Yang, A. M. Nardes, C. C. Mercado, S. Ferrere, M. O. Reese, W. Zhou, K. Zhu, Chemistry of Materials 2015, 27, 4814-4820.
 C. Yi, J. Luo, S. Meloni, A. Boziki, N. Ashari-Astani, C. Gratzel, S. M. Zakeeruddin, U. Rothlisberger, M. Gratzel, Energy & Environmental Science 2016, 9, 656-662.
9:15 AM - ES1.14.02
Complex-Assisted Gas Quenching as a Universal Deposition Method for Single, Double, Triple and Quadruple Cation Perovskite Solar Cells with High Efficiency
Bert Conings 1 2 , Aslihan Babayigit 1 2 , Matthew Klug 2 , Sai Bai 2 3 , Nicolas Gauquelin 4 , Nobuya Sakai 2 , Jacob Wang 2 , Johan Verbeeck 4 , Hans-Gerd Boyen 1 , Henry Snaith 2 Show Abstract
1 , Hasselt University - Materials Research Institute, Diepenbeek Belgium, 2 , University of Oxford, Oxford United Kingdom, 3 , Biomolecular and Organic Electronics, Linköping Sweden, 4 , University of Antwerp - Electron Microscopy for Materials Science (EMAT), Antwerp Belgium
In the course of the experimental developments in perovskite absorber layers, a plethora of strategies has arisen to tune their thin film qualities for the purpose of high efficiency devices. Despite this wealth of deposition approaches, the community experiences a great deal of irreproducibility from laboratory to laboratory and between different preparation methods. Another remarkable point is that the viability of most –if not all– film enhancement strategies through deposition and precursor tweaking has been initially established by demonstrating the successful operation of one particular type of perovskite solar cells (both in terms of composition and device architecture), but they typically require rigorous optimization when applied for different perovskite compositions and device architectures. These generally encountered observations in perovskite research illustrate the need for a universal and uncomplicated deposition strategy that is applicable for many compositions of perovskite, and also insensitive to minor changes in deposition conditions. To this end, we developed Complex-Assisted Gas Quenching (CAGQ), a robust and expedient method for the solution deposition of hybrid perovskite thin films. We present regular and inverted solar cells based on single, double, triple and quadruple cation perovskites, fabricated using CAGQ, all delivering state-of-the-art efficiencies. With this, CAGQ offers a reliable standard practice for the fabrication of a non-exhaustive variety of perovskites exhibiting excellent film morphology and corresponding high performance. We provide a detailed account of the practicalities of the technique, as well as a critical view on the nanocrystalline properties of the thus prepared perovskite films.
1. A. Sjarenko and M.F. Toney, J. Am. Chem. Soc., 2016, 138, 463-470.
2. J. Berry et al., Adv. Mater. 2015, 27, 5102-5112.
9:30 AM - ES1.14.03
Purely Oriented Crystalline Organolead Halide Perovskite Films
Nam Chul Cho 1 3 , Feng Li 1 , Bekir Turedi 1 , Lutfan Sinatra 1 , Smritakshi Sarmah 1 , Manas Parida 1 , Makhsud Saidaminov 1 , Banavoth Murali 1 , Victor Burlakov 2 , Alain Goriely 2 , Omar Mohammed 1 , Tom Wu 1 , Osman Bakr 1 Show Abstract
1 Materials Science and Engineering, King Abdullah University of Science and Technology, Thuwal Saudi Arabia, 3 Department of Energy System, Soonchunhyang University, Asan Korea (the Republic of), 2 Mathematical Institute, University of Oxford, Oxford United Kingdom
Methylammonium lead iodide perovskites (MAPbI3) have interesting optical and electrical properties that have been intensively studied for a broad range of optoelectronic applications such as solar cells, photodetectors, light-emitting diodes, and lasing applications. It is also a good light absorbing material, having direct band gap of 1.55 eV, with a small exciton binding energy of approximately 0.03 eV leading to efficient dissociation of photogenerated charge carriers at room temperature. Furthermore, the photogenerated electrons and holes have a small effective mass, giving rise to high carrier mobility of approximately 10 – 20 cm2 V-1s-1, while the recombination lifetime of hundreds of nanoseconds results in long diffusion lengths of charge carriers as high as 2-3 micrometers. These appealing properties motivated researchers to explore not only the engineering of material’s composition and film-deposition process, but also to investigate some extraordinary properties of these materials such as a giant dielectric constant under light illumination and the massive migration of ions.
These optical and electronic properties of the perovskite films are closely correlated to the crystal orientation and nano- or macro-meter scale of film morphologies. In particular, single crystal perovskites exhibit extraordinary optoelectronic properties compared to the generally reported polycrystalline perovskite films. Unfortunately, single crystal based perovskite films are extremely challenging to fabricate and would be a game changer in the field of solution processed optoelectronics, if they could be realized.
Here we present a large area, mass-producible, and sub 2-3 micrometer-thin perovskite films of pure crystal orientation. We will discuss the methods to control the orientation of the perovskite crystals and their macroscopic morphology, as well as explore the transport and photophyiscal properties of these films and demonstrate their promising applications in lasing and field-effect transistors. Specifically, orientationally pure crystalline (OPC) MAPbI3 hybrid perovskite film was fabricated using a thermal-gradient-assisted directional crystallization method. We found that this process relies on the sharp liquid-to-solid transition of MAPbI3 from ionic liquid solution. This OPC films spontaneously form periodic microarrays that are clearly distinguishable from general polycrystalline perovskite materials in terms of their crystal orientation, film morphology, and electronic properties. Interestingly, the OPC film is strongly oriented in the (112) and (200) planes parallel to the substrate and shows intense anisotropy in charge transport. We believe that the ability to control crystal orientation and morphology could be widely applicable in various optoelectronic devices.
9:45 AM - ES1.14.04
Controlling Growth Thermodynamics and Phase Stability through Rational Compositional Engineering of Hybrid Organic-Inorganic Perovskites
Spencer Williams 1 , Adharsh Rajagopal 1 , Alex Jen 1 Show Abstract
1 Materials Science and Engineering, UW, Seattle, Washington, United States
One of the primary problems facing the scale of up perovskite photovoltaics is the difficulty in growing high quality films in the solvent rich environment created through techniques like blade and roll to roll coating. The thermodynamically limited perovskite growth these conditions create has been a significant hurdle in adapting techniques for perovskite growth developed on the lab scale to techniques for large area deposition. Without the kinetic controls used in lab scale deposition techniques like spin casting, resulting perovskite films in general have poor coverage and crystallinity. We have identified that these issues are directly due to the influence of the solvent molecule and the resulting formation of the well-known DMSO-perovskite intermediate phase.
Through transition metal modification of the hybrid perovskite lattice, we have enabled the first documented route enabling direct perovskite nucleation and growth at room temperature. We show that direct perovskite nucleation naturally generates high quality thin films, even in thermodynamically limited growth with no heating at room temperature. Although we show that transition metal modification enables direct perovskite nucleation which addresses the larger concern of adapting perovskite synthesis to large area techniques, we also establish how transition metal modification enables fundamentally new functionality and impacts optoelectronic properties.
10:00 AM - ES1.14.05
Controlling Nucleation, Growth, and Orientation of CH3NH3PbI3 Perovskite Thin Films with Rationally Selected Additives
Benjamin Foley 1 , Justin Girard 1 , Blaire Sorenson 2 , Alexander Chen 1 , Scott Niezgoda 1 , Matthew Alpert 1 , Angela Harper 3 , Detlef Smilgies 2 , Paulette Clancy 2 , Wissam Saidi 4 , Joshua Choi 1 Show Abstract
1 , University of Virginia, Charlottesville, Virginia, United States, 2 , Cornell University, Ithaca, New York, United States, 3 , Wake Forest University, Winston-Salem, North Carolina, United States, 4 , University of Pittsburgh, Pittsburg, Pennsylvania, United States
Solution processable photovoltaic materials hold promise for the development of solar cells that combine high power conversion efficiency and low-cost. Among these materials, metal halide perovskites (MHPs) have the potential to revolutionize the photovoltaics industry with their record power conversion efficiency of 22%. However, further improvements in solar cell efficiency, long-term stability, and large scale device manufacturing at industrially relevant levels are currently limited by a poor understanding of the MHP thin film self-assembly processes. Recent works have shown that photovoltaic parameters vary greatly with crystal orientation, and that both solar cell efficiency and stability can improve with increased grain size. Therefore, a more thorough understanding of the fundamental relationship between solution chemistry and crystallization process is needed to achieve better morphology with controlled grain size and orientation.
Here we investigate the impact of rationally selected chemical additives in precursor solutions on the nucleation and growth of methylammonium lead iodide perovskite thin films. Computational screening was performed to guide the selection of tetrahydrothiopene oxide as an additive with much stronger solvation efficacy than all other commonly used solvents, including DMSO. In-situ grazing incidence X-ray diffraction measurements show that the additives suppress the formation of homogeneous nuclei as well as crystalline intermediate structures. Instead, heterogeneous nucleation as sparse as 1 per square millimeter occurs on the substrate surface and a tetragonal (100) oriented film grows directly from the precursor solution. Our density functional theory calculations show that the crystallographic orientation of the thin films can be tuned by altering the surface energies via adsorption of chemical additives. The crystallographic orientation of the thin films was found to have a significant impact on the open circuit voltage of solar cell devices, highlighting the importance of controlling the metal halide perovskite thin film orientation.
The systematic demonstrated in this work will enable more efficient and robust selection of MHP precursor solution formation, leading to more precise degree of control over MHP thin film formation processes. Ultimately, these advances will contribute to accelerating the progress in MHP solar cell efficiency improvement, scale-up of device manufacturing, better stability and reliability.
10:15 AM - ES1.14.06
A Low Viscosity, Low Boiling Point, Clean Solvent System for the Rapid Crystallisation of Highly Specular Perovskite Films
Nakita Noel 1 , Severin Habisreutinger 1 , Bernard Wenger 1 , Matthew Klug 1 , Maximilian Hoerantner 1 , Michael Johnston 1 , Robin Nicholas 1 , David Moore 1 2 , Henry Snaith 1 Show Abstract
1 , University of Oxford, Oxford United Kingdom, 2 , National Renewable Energy Laboratory, Denver, Colorado, United States
Perovskite-based photovoltaics have immense potential to totally transform the solar industry. While there are many ways in which this material can be deposited, spin-coating remains one of the simplest methods to obtain high efficiency perovskite solar cells. While this is not the ideal method for large scale manufacturing, it is a starting point from which more scalable methodologies can be developed, for example, ink-jet printing or slot-die coating. Here, in place of the commonly used strongly coordinating, aprotic solvents, we use a new, solvent system with a low viscosity and a low boiling point. The use of this solvent enables rapid, room temperature crystallisation of methylammonium lead triiodide perovskite films. We are able to produce dense, pinhole free films with uniform coverage, high specularity, and enhanced optoelectronic properties. We fabricate devices and achieve stabilised power conversion efficiencies of over 18 % for films which have been annealed at 100°C, and over 17 % for films which have been dried under vacuum and have undergone no thermal processing. This deposition technique allows uniform coating on substrate areas of up to 125 cm2, and additionally on devices with a 1 cm2 active area, yield also yield efficiencies of up to 17 % . This new processing route has remarkable potential for the fabrication of large area, high efficiency, solution processed devices, and represents a critical step towards industrial upscaling and large area printing of perovskite solar cells.
10:30 AM - ES1.14.07
Meniscus-Assisted Solution Printing of Perovskite Solar Cells
Ming He 1 , Beibei Jiang 1 , Yanjie He 1 , Zhiqun Lin 1 Show Abstract
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Crystal control of metal halide perovskite films is of importance to high performance optoelectronic applications. However, this is particularly challenging for solution printed devices due to complex crystallization kinetics of perovskites in dynamic ink flows. Here we described a robust meniscus-assisted solution printing (MASP) approach to perovskite films with micrometer-scale grains, good crystallization, and preferential orientation. Central to this strategy is the solvent evaporation-triggered outward convective flow that transported the perovskite solutes to the edge of the meniscus, thus promoting the perovskite crystallization. The kinetics of crystal growth was elucidated by in-situ optical microscopy tracking for further understanding the crystallization mechanism of perovskites during the solution printing process. The perovskite films produced by MASP exerted excellent optoelectronic properties such as long carrier lifetimes, low trap-state densities, and eventually high efficiencies approaching 20 % in planar solar cells. We anticipate this MASP strategy to promote the future commericialization of perovskites in solution printed optoelectronic devices.
11:15 AM - ES1.14.08
Methylamine Vapor-Annealing on MAPbI3 Perovskite Improves Device Stability and Efficiencies up to 18.4%
Yan Jiang 1 , Emilio Juarez-Perez 1 , Qianqing Ge 2 , Shenghao Wang 1 , Matthew Leyden 1 , Luis Ono 1 , Sonia Raga 1 , Jinsong Hu 2 , Yabing Qi 1 Show Abstract
1 Energy Materials and Surface Sciences Unit (EMSS), Okinawa Institute of Science and Technology Graduate University (OIST), Okinawa Japan, 2 CAS Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry Chinese Academy of Sciences, Beijing China
High power conversion efficiencies (PCEs) and long lifetime are the major pre-requisites for perovskite solar cells to further advance to the next stage. The quality of perovskite films is one of the most important factors. In this work, methylamine vapor-annealing was performed on MAPbI3 perovskite. We find that many grain boundary (GB)-related issues are solved with the methylamine vapor-annealing, compared to thermally or solvent annealing treatments. Our results show that (I) surface impurities at GBs are greatly reduced and carrier recombination within the perovskite layer (i.e. intra-layer carrier recombination) is suppressed; (II) disconnected grains that would otherwise be formed during residual solvent evaporation are avoided and the direct contact between the electron transporting layer and hole transporting layer is nearly eliminated, as a result of which carrier recombination between separate layers (i.e. inter-layer carrier recombination) is reduced. The detailed study on these two types of carrier recombination processes provide valuable guidelines for recombination kinetics analyses, which are necessary to better understand perovskite solar cells device operation. The perovskite solar cell device results show that methylamine vapor-annealing not only significantly improves solar cell efficiency but also device stability. Furthermore, the methylamine vapor-annealing treatment has the advantages of easy processability and high reproducibility, which is expected to be applicable for perovskite films prepared by a wide variety of different fabrication methods.
 Y. Jiang, E. Juarez-Perez, Q. Ge, S. Wang, M. R. Leyden, L. K. Ono, S. R. Raga, J. Hu, and Y. B. Qi*, Mater. Horiz. 2016, DOI: 10.1039/c6mh00160b.
11:30 AM - ES1.14.09
‘Soft’ Processing of Hybrid Perovskites
Yuanyuan Zhou 1 , Kai Zhu 2 , Shuping Pang 3 , Nitin Padture 1 Show Abstract
1 School of Engineering, Brown University, Providence, Rhode Island, United States, 2 Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado, United States, 3 Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao China
Hybrid organic-inorganic perovskites (HOIPs) are a group of crystalline materials with rotating molecular cations located inside an inorganic framework. Such unique compositions and structures make HOIPs inherently ‘soft’ compared with traditional inorganic materials.1 Here, we have discovered that organic gases such as methylamine or formamidine can interact actively with HOIPs, which can cause transformative changes in morphologies and/or compositions of HOIPs. The exploration of these organic-gas/HOIP interaction behavior has inspired a series of unconventional synthetic protocols 2-5 for the creation of HOIP thin films with desirable compositions and morphologies (ultra-smoothness, beneficial grain structures, etc.), which have shown exceptional promise for the scaling-up of perovskite solar cells (PSCs). A series of in-situ and ex-situ characterization (optical/photoluminescence microscopy, TEM, XRD, etc.) experiments are conducted to understand the underlying mechanisms, which is opening up ‘uncharted territory’ in chemistry and materials science.
1. Y. Zhou, O.S. Game, S. Pang, N.P. Padture. Journal of Physical Chemistry Letters, 2015, 6, 4827-4839.
2. Y. Zhou, M. Yang, S. Pang, K. Zhu, N.P. Padture. Journal of American Chemical Society, 2016, 138, 5535-5538
3. S. Pang, Y. Zhou, Z. Wang, M. Yang, A.R. Krause, K. Zhu, N.P. Padture, G. Cui. Journal of American Chemical Society, 2016, 138, 750-753
4. Z. Zhou, Z. Wang, Y. Zhou, S. Pang, H. Xu, Z. Liu, N.P. Padture, G. Cui. Angewandte Chemie International Edition, 2015, 54, 9705-9709.
5. Y. Zong, Y. Zhou, M.-G. Ju, H. F. Garces, A. R. Krause, F. Ji, G. Cui, X. C. Zeng, N. P. Padture, S. Pang. Angewante Chemie International Edition, 2016, 47,14723-14727
11:45 AM - ES1.14.10
Microwave Near-Field Imaging and Morphology of Perovskite Photovoltaics
Samuel Berweger 1 , Gordon MacDonald 1 , Mengjin Yang 2 , Kevin Coakley 1 , Joseph Berry 2 , Kai Zhu 2 , Frank DelRio 1 , Thomas Wallis 1 , Pavel Kabos 1 Show Abstract
1 , National Institute of Standards and Technology, Boulder, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Perovskite photovoltaics have made rapid advances in performance in recent years, in part due to the robustness of device performance to morphological variations of the CH3NH3PbI3 (MAPI) active layer. However, these morphological variations together with the rapid deterioration of pristine films also present a challenge to understanding the relationship between the complex film morphology, the associated electronic variations, and the resulting device performance. Here we use scanning microwave microscopy (SMM) together with correlated photoluminescence (PL) mapping to study the morphology and spatially-resolved electronic properties of pristine and degraded MAPI films processed at varying ambient humidity. We find that increasing the processing humidity directly affects the grain boundary conductivity while the grains themselves remain largely spatially uniform. However, films degraded by exposure to ambient conditions show significant spatial variations in conductivity with degradation proceeding preferably at the grain boundaries as well as nanometer-sized features within individual grains. Lastly, our PL shows little spatial variation across grain boundaries, but spectral lineshape analysis suggests variations in photon recycling across the films related to long-range PL intensity variations.
12:00 PM - ES1.14.11
Formulating Perovskite Precursor Inks for Scale-Up
Mengjin Yang 2 , Joseph Berry 1 , Maikel Van Hest 1 , Kai Zhu 2 Show Abstract
2 Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado, United States, 1 Material Science Center, National Renewable Energy Laboratory, Golden, Colorado, United States
Over the last couple of years, lead halide perovskites absorbers have emerged as a promising contender for the future photovoltaic market. Unprecedented efficiency improvements have been achieved using the lab-scale spin coating technique. However, there is still a wide gap between spin coating and scalable deposition methods (such as blade coating, slot die, spray, inkjet printing, electrochemical deposition), making it challenging to reach its promising efficiency in mass production. The discrepancy between these techniques mainly lies in the different final perovskite film morphologies caused by vast distinctive casting/drying/crystallization/conversion mechanisms. The precursor ink chemistry (solvent, coordination chemistry) of perovskite for scale-up deposition is critical, but has been underexplored. We present a rational design of perovskite precursor film formation to achieve highly specular film using scalable deposition methods. Device efficiency has also been improved considerably with high quality perovskite films. This finding makes a significant advance towards commercialization of the perovskite photovoltaic technology.
12:15 PM - ES1.14.12
Compact-TiO2 Deposited via ALD for Highly-Repeatable and Low-Hysteresis Perovskite Solar Cells
Arun Chouhan 1 , Naga Prathibha Jasti 1 , Raghunandan Iyer 2 , Sushobhan Avasthi 1 Show Abstract
1 Centre for Nanoscience and Engineering, Indian Institute of Science, Bangalore, Karnataka, India, 2 Department of Energy Science and Engineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
Two issues plaguing large-area perovskite solar cells are low device-to-device reproducibility and hysteresis in current-voltage characteristics. Pinholes and defects in the spin-coated compact-TiO2 layer, which is the most common electron-transport layer, can explain atleast some of the devices variability and hysteresis. In this work, we report a novel compact-TiO2 layer, deposited using atomic layer deposition (ALD), which is more conformal, pin-hole free and less-defective over large-areas, than TiO2 deposited via spin coating or thermal oxidation of Ti metal. Consequently, devices with c-TiO2 deposited via ALD show reduced hysteresis and device-to-device variability than device with c-TiO2 deposited using other processes. The ALD-TiO2 devices show an efficiency of ~10.0%.
Compact-TiO2 was deposited on FTO glass using 3 methods: a) thermally oxidized c-TiO2 formed by oxidizing titanium metal film in air at 500oC (40nm), b) spin-coated c-TiO2 followed by 500oC anneal, using titanium isopropoxide as the precursor (~100 nm), and c) ALD c-TiO2 deposited at 200oC using titanium (IV) isopropoxide and H2O as precursors (43 nm). SEM showed that spin-coated and oxidized c-TiO2 were relatively non-uniform films and with dendrites and pinholes. In comparison, ALD c-TiO2 layers were very conformal, following the morphology of the underlying FTO substrate, and had no pinholes. Pure-halide solar cells were fabricated with the three c-TiO2 layers, using a FTO/c-TiO2/mesoTiO2-perovskite/spiro-OMeTAD/Au structure. Devices with oxidized c-TiO2 showed very large hysteresis with ΔJsc as high as 11 mA/cm2 between forward and reverse scans. Device-to-device variability was also very high with efficiency varying from 5% to 15%. Cells with spin-coated c-TiO2 showed smaller hysteresis with ΔJsc of around 3mA/cm2 in forward and reverse scans. Device-to-device variability was as bad as oxidized c-TiO2. In comparison, ALD c-TiO2 based devices showed negligible hysteresis with ΔJsc of 1mA/cm2. Device-to-device variation was also very low with efficiency varying from 7% to 10%. The Voc of the ALD C-TiO2 devices was ~930mV, further confirming the absence of pin-holes.
In conclusion, we show that compact TiO2 deposited using ALD significantly reduces the hysteresis and device-to-device variation of perovskite solar cells as compared to TiO2 deposited through spin coating and thermal oxidation of Ti metal. ALD TiO2 is a better candidate for electrons-transport layer for large-area perovskite devices.
12:30 PM - ES1.14.13
All Vapor-Deposited Lead-Free Doped CsSnBr3 Planar Solar Cells
Dhanashree Moghe 1 , Lili Wang 1 , Christopher Traverse 1 , Adam Redoute 1 , Melany Sponseller 2 , Patrick Brown 2 , Vladimir Bulovic 2 , Richard Lunt 1 Show Abstract
1 , Michigan State University, East Lansing, Michigan, United States, 2 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
One of the key impediments to the commercialization of lead-based hybrid perovskite is toxicity caused by water-soluble lead. Therefore we have turned our attention to the demonstration of stable non-lead based alternatives via all thermal vapor-deposited planar CsSnBr3 perovskite solar cells. In this work, the cell architecture consists of a planar CsSnBr3 heterojunction where the perovskite layer is grown by thin film sequential deposition of SnBr2 and CsBr allowing for immediate reaction. This represents one of the highest efficiency all-inorganic bromide perovskite devices without lead and with all the layers prepared via vapor deposition. While other halides of CsSnX3 with Cl and I are extremely air sensitive and change color within seconds, illumination tests performed on the unencapsulated CsSnBr3 devices in air show no change over many hrs. Further, we evaluate the impact of low-temperature annealing, and incorporation of fluoride doping via vapor deposition. Our results show that the CsSnBr3 perovskite films can be adequately doped via vapor deposition, leading to enhancements in quantum efficiency and a doubling of overall performance. Using depth resolved XPS we also show that the device performance is not particularly sensitive to the position or distribution of the dopant layer, which shows generally uniform diffusion of the dopant throughout the film even with neat layers of the dopants grown at various positions. This work could provide new pathways for the doping and deposition of a wide range of all-inorganic halide perovskites and highlights an important and air stable perovskite solar cell candidate.
12:45 PM - ES1.14.14
Perovskite Solar Cells on Flexible Glasses
Benjia Dou 1 2 , Frank Barnes 2 , Sean Shaheen 2 3 , Sean Garner 4 , Maikel Van Hest 1 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States, 2 Department of Electrical, Computer and Energy Engineering, University of Colorado Boulder, Boulder, Colorado, United States, 3 Renewable and Sustainable Energy Institute, University of Colorado Boulder, Boulder, Colorado, United States, 4 , Corning Incorporated, Corning, New York, United States
Metal halide perovskites have recently emerged as a highly promising solar cell technology with high light to electricity power conversion efficiency and low processing cost due to their solution processability. However, to make perovskite solar cells commercially viable, particularly to compete with or build upon the traditional silicon dominated photovoltaic market, substantial progress is needed in improving their process techniques and scalability. Fabricating perovskite devices and modules in a roll-to-roll process on flexible substrates will enable high throughput manufacturing, and it will also allow the application space to be extended beyond what is available to rigid geometries. Here, we investigated the performance of flexible perovskite solar cells with various transparent conductors, includes flexible indium tin oxides (ITO) and indium zinc oxides (IZO), on thin (100μm) flexible glass substrates. These are compared to devices fabricated on rigid glass, using standard fluorine doped tin oxide (FTO) and ITO as the transparent conductors. Challenges of scaling up perovskites to larger area on flexible substrates are also studied. For a device structures of flexible ITO/TiO2/mixed cation perovskites/Spiro-OMeTAD/MoOx/Al, a power conversion efficiency of 13% was demonstrated.
ES1.15: Fundamental, Spectroscopy and Hysteresis
Friday PM, April 21, 2017
PCC North, 200 Level, Room 224 B
2:30 PM - ES1.15.01
Local Structure Effects in Hybrid Organometal Trihalide Perovskites Probed by High Energy Resolution X-Ray Spectroscopy
Walter Drisdell 1 , Linn Leppert 1 , Carolin Sutter-Fella 2 , Yufeng Liang 1 , Yanbo Li 3 , Quynh Ngo 2 , Sheraz Gul 1 , Thomas Kroll 4 , Dimosthenis Sokaras 4 , Ali Javey 2 , David Prendergast 1 , Francesca Maria Toma 1 , Ian Sharp 1 Show Abstract
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 , University of California, Berkeley, Berkeley, California, United States, 3 , University of Electronic Science and Technology of China, Chengdu China, 4 , SLAC National Accelerator Laboratory, Menlo Park, California, United States
Hybrid organometal tridhalide perovskites show great promise for use in tandem solar cells due to their high efficiencies, inexpensive synthesis, and high degree of tunability. Band gaps can be tuned by varying the halide composition, cation composition, or divalent metal, with certain mixtures also demonstrating enhanced stability. Fundamental understanding of the origins of these effects, however, is lacking. We present a high energy resolution fluorescence detection (HERFD) X-ray absorption spectroscopy (XAS) study of perovskites with different halide and cation compositions. The high resolution of this technique reveals strong spectral sensitivity to local structure in these materials. By coupling to first-principles density functional theory (DFT) computations, we are able to connect spectral response to local atomic and electronic structure on the order of a single metal halide octahedron. We discuss the interplay between atomic and electronic structure in perovskite materials as a function of halide composition, as well as cation interactions with the metal centers, and how these relate to performance and device properties.
2:45 PM - ES1.15.02
Carrier Dynamics of Organic-Inorganic Hybrid Lead Iodide Perovskites Probed by Electron-Rotor Interactions
Jue Gong 1 , Mengjin Yang 2 , Xiangchao Ma 3 , Richard Schaller 4 , Gang Liu 5 , Lingping Kong 5 , Ye Yang 2 , Matthew Beard 2 , Michael Lesslie 1 , Ying Dai 3 , Baibiao Huang 3 , Kai Zhu 2 , Tao Xu 1 Show Abstract
1 Department of Chemistry & Biochemistry, Northern Illinois University, DeKalb, Illinois, United States, 2 Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado, United States, 3 School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan, Shandong, China, 4 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 5 , Center for High Pressure Science and Technology Advanced Research, Shanghai China
Electron-lattice interaction governs the fundamental working principles of multiple energy materials, and modifications of the lattice characteristics may give rise to different material properties, such as superconductivity, thermoelectricity, photovoltaics and supercapacitors. Being an outstanding light-harvesting active material for photovoltaic purpose, methylammonium lead iodide (CH3NH3PbI3, or MAPbI3) is composed of two parts—inorganic framework PbI3- that extends three-dimensionally, and intercalated cation MA+ that is electrostatically pinned in the voids formed by PbI6 octahedra in proximity. Distinctively, MA+ also undergoes rotational motions that results in spatial reorientation of the cationic charge. Therefore, it is intriguing to reveal the perturbation of photocarrier dynamics that exclusively occurs in the inorganic sublattice, by tuning the rotational frequency of organic MA+. Herein, hydrogen atoms in methyl group and/or ammonium group were substituted by deuterium atoms to modulate the rotational frequency of MA+ while keeping its chemical nature and electronic structure intact. Strikingly, time-resolved photoluminescence studies configured a significant difference in carrier lifetimes among CH3NH3PbI3, CH3ND3PbI3, CD3NH3PbI3 and CD3ND3PbI3 single crystals. To account for such phenomenon, a polaron model of photocarriers was established. DFT calculations reveal the density of states of CH3NH3PbI3 near band edges and polaron trapping energies are highly dependent on MA+ orientation. The discovery of electron-rotor interaction in hybrid lead iodide perovskites should provide a theoretical foundation in the quest for better photovoltaic performance.
3:00 PM - ES1.15.03
Hybrid Perovskite Phase Transition and Its Ionic, Electrical and Optical Properties under Normal Solar Cell Operation
Md Nadim Ferdous Hoque 1 , Nazifah Islam 1 , Zhen Li 2 , Kai Zhu 2 , Zhaoyang Fan 1 Show Abstract
1 Electrical & Computer Engineering, Texas Tech University, Lubbock, Texas, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Practical hybrid perovskite solar cells (PSCs) must endure temperatures above the tetragonal-cubic structural phase transition of methylammonium lead iodide (MAPbI3) that occurs at 40-60 oC. However, the ionic, electrical and optical properties of MAPbI3 in such a temperature range, and particularly, whether the structural phase transition could result in dramatic changes in these properties, are not well studied. In addition, how the film morphology including the grain size and grain boundaries impact on ionic transportation is not well known. Herein, we report a striking contrast at ~45 oC in the ionic/electrical properties of MAPbI3 due to a change of the ion activation energy from 0.7 eV to 0.5 eV, whereas the optical properties exhibit no particular transition except for the steady increase of the bandgap with temperature. These observations can be explained by the “continuous” nature of perovskite phase transition. We speculate that the critical temperature at which the ionic/electrical properties change, although related to crystal symmetry variation, is not necessarily the same temperature when tetragonal-cubic structural phase transition occurs. The dependence of the ionic and electrical properties on grain size will also be reported.
3:15 PM - ES1.15.04
Understanding the Effect of Band Alignment and Surface States on the Hysteresis and Response Time of TiO2-Based Perovskite Solar Cells
Heping Shen 1 , Yiliang Wu 1 , Daniel Jacbos 1 , The Duong 1 , Xiaoming Wen 2 , Xiao Fu 1 , Jun Peng 1 , Siva Karuturi 1 , Shakir Rahman 1 , Klaus Weber 1 , Kylie Catchpole 1 , Thomas White 1 Show Abstract
1 , Australian National University, Canberra, Australian Capital Territory, Australia, 2 , University of New South Wales, Sydney, New South Wales, Australia
Hysteresis has been reported as a notorious issue for perovskite solar cells (PSCs), which makes it difficult to provide a reliable value of the power conversion efficiency (PCE) and the maximum power output. Therefore, unveiling the origin of the hysteresis behavior of perovskite solar cells and understanding the underlying physical mechanisms is of profound importance. In this work, we investigate the effect of band alignment of the TiO2/perovskite interface and the effect of TiO2 surface states by varying the preparation method of both the perovskite and TiO2 layer.
First, one-step method and modified two-step method are employed to prepare the CH3NH3PbI3 perovskite film leading to distinctly different hysteresis behavior. The perovskite based on the latter method exhibits so-called “inverted hysteresis” with better cell performance on forward scanning than reverse scanning. We show using numerical simulation incorporating an ion diffusion-drift model that this is due to positive ion accumulation (positive ions on the electron transport material (ETM)/Perovskite side and negative ions on the hole transport material (HTM)/perovskite), leading to detrimental (upward) band bending in the perovskite layer and hence high surface recombination and smaller current. The detrimental band bending is even more severe when the TiO2/perovskite interface shows a larger offset, contributing mainly to the “inverted hysteresis”.
Second, compared to the solution based method, TiO2 compact layer deposited by the ALD method leads to substantially less hysteresis, accompanied with a dramatically diminished response time. In detail, the time constant of the slow component, fitted from the transient current density by switching the device from open-circuit to short-circuit, exhibited 5-fold reduction, while a much more remarkable decrease (more than 20-fold) occurred for the fast decay component. Two mechanisms are proposed to explain how the contact material induces such an effect by interacting with the perovskite. The lower doping level of the ALD compact layer leads to a larger work-function (of absolution value versus vacuum level), indicating less ion migration due to reduced built-in voltage. In addition, time-resolved transient surface photovoltage (SPV) investigation on the surface states of TiO2 films reveals that the surface traps can also play a vital role by either altering the time-scale of the cell by the slow charging and discharging processes, or by interacting with the ion migration simultaneously during the operation of the cell.
The investigations carried out in this work demonstrate that there is scope to engineer the hysteresis and response time of TiO2/perovskite solar cells using the fabrication method of both the perovskite and TiO2, and that low levels of hysteresis and fast response time can be achieved by paying attention to the band alignment of the interface and the doping and density of surface states in the TiO2.
3:30 PM - ES1.15.05
Determining Band-Edge Energies and Morphology-Dependent Stability of Formamidinium Lead Perovskite Films Using Spectroelectrochemistry and Photoelectron Spectroscopy
R. Shallcross 1 , Yilong Zheng 1 , S. Scott Saavedra 1 , Neal Armstrong 1 Show Abstract
1 Chemistry and Biochemistry, University of Arizona, Tucson, Arizona, United States
We show for the first time how solution-phase spectroelectrochemistry, which probes the buried perovskite/contact interface, can be used to characterize the frontier orbital (e.g., conduction band) energetics of solar-cell-relevant hybrid formamidinium lead trihalide perovskite (FAPbX3) films on metal oxide (e.g., ITO and TiO2) contacts. The methylammonium bromide (MABr)-doped FAPbX3 thin films interrogated here are processed via a DMSO-adduct approach and are representative of high-performance hybrid perovskites that have afforded photovoltaic (PV) device power conversion efficiencies in excess of 20%. We compare and contrast these electrochemically-determined energetics with more traditional ultraviolet photoelectron spectroscopy (UPS) measurements, which probe the perovskite/vacuum interface and provide direct estimates of the valence band energy.
The electrochemically-induced electron injection process leads to inter-grain (i.e., grain boundary) dissolution and intra-grain pitting of these thin films and reveals the heterogeneity in grain-to-grain stability and electroactivity. In order to better understand these dissolution processes, we characterize the morphology, structure, and surface chemical composition of these films as a function of the extent of electrochemical reduction (i.e., the amount of injected charge) using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. These measurements demonstrate that, while the bulk crystal structure (XRD) remains purely perovskite (trigonal, <101> orientation), the grain boundary regions are the least stable components of the perovskite active layer, and that adjacent grains, which might appear to be identical, can have significantly different electroactivities and stabilities.
These electrochemically-driven experiments provide a unique approach to understanding the band-edge energetics and morphology-dependent stability and, thus, afford a novel means for characterizing and optimizing these promising hybrid perovskite materials. The ability to understand the interfacial energetics and composition of these next generation materials on nanometer to micron length scales is necessary to ensure scaling of PV platforms without significant loss in performance and/or long-term stability.
ES1.16: Synthesis, Nanoparticles and Single Crystal
Friday PM, April 21, 2017
PCC North, 200 Level, Room 224 B
4:30 PM - ES1.16.01
Perovskite CH3NH3PbI3(Cl) Single Crystals—Rapid Solution Growth, Large Size, State-of-the-Art Crystalline Quality and Low Trap Density towards 108 cm-3
Zhipeng Lian 1 , Qingfeng Yan 1 Show Abstract
1 Department of Chemistry, Tsinghua University, Beijing China
Single crystal reflects the intrinsic physical properties of a material and single crystals with high-crystalline quality are highly desired for the acquisition of high-performance devices. However, it is always challenging to obtain commercially desired single crystal materials with a combination of large size, rapid growth rate and high crystalline quality. We have employed chlorine promoters to realize the rapid growth of MAPbI3(Cl) single crystal with ultra-high quality. In our finding, chlorine promoters not only shorten the synthetic time (from one month to a few days to harvest larger crystal) but also help with the crystalline perfection, thus leading to a considerable low cost and energy saving in manufacturing materials and devices. Within 5 days, CH3NH3PbI3(Cl) single crystal as large as 20 mm × 18 mm × 6 mm was harvested. As a most important index to evaluate the crystalline quality, the full-width at half maximum (FWHM) in the high-resolution X-ray rocking curve (HR-XRC) of as-grown CH3NH3PbI3(Cl) single crystal was measured as 20 arcsec. Such high structural perfections contributed to much lower trap-state density 7.6 × 108 cm-3 (an order of magnitude lower than previously reported), high carrier mobility of 167 ± 35 cm2 V-1s-1, and long transient photovoltaic carrier lifetime of 449 ± 76 μs. The improvement in the crystalline quality, together with the rapid growth rate and excellent carrier transport property, provides state-of-the-art single crystalline hybrid perovskite materials for high-performance optoelectronic devices.
4:45 PM - ES1.16.02
Molecularly Engineered Phthalocyanines as Charge-Transporting Materials in Perovskite Solar Cells
Olga Trukhina 1 2 , Kyung Taek Cho 1 , Cristina Roldancarmona 1 , Mine Ince 3 , Paul Gratia 1 , Giulia Grancini 1 , Peng Gao 1 , Tomas Torres 2 4 , Mohammad Nazeeruddin 1 Show Abstract
1 , EPFL Valais, Sion Switzerland, 2 , Autonoma University of Madrid, Madrid Spain, 3 , Mersin University, Mersin Turkey, 4 , IMDEA Nanociencia, Madrid Spain
Phthalocyanines (Pcs) are planar, conjugated macrocycles which possess outstanding electrical and optical properties that make them perfect candidates for their incorporation into perovskite solar cells as charge-transporting materials. Although several reports have appeared on the fabrication of Pc-based devices, only moderate photovoltaic performance has been achieved, considering the interface morphology to be the major factor.
Here, we report the novel examples of substituted macrocycles as charge-transporting materials in mixed-ion perovskite [HC(NH2)2]0.85(CH3NH3)0.15Pb(I0.85Br0.15)3 solar cells, reaching 17.5% - the highest power conversion efficiency reported so far for phthalocyanines. Results confirmed that the photovoltaic performance is strongly influenced by both, the individual optoelectronic properties of the compounds and the aggregation of these tetrapyrrolic semiconductors in the solid thin film. These results boost up the potential of solution-processed Pcs derivatives as stable and economic charge-transporting materials for large-scale applications, opening up new frontiers towards a realistic, efficient and inexpensive energy production.
5:00 PM - ES1.16.03
Long-Lived Carriers Found in Double Metal Lead-Free Halide Perovskite by Time-Resolved Microwave Conductance Measurements
Davide Bartesaghi 1 2 , Adam Slavney 3 , Hemamala Karunadasa 3 , Tom Savenije 1 Show Abstract
1 , Delft University of Technology, Delft Netherlands, 2 , M2i, Delft Netherlands, 3 , Stanford University, Stanford, California, United States
Lead-halide perovskites have recently attracted much attention due to their applicability in highly efficient photovoltaic devices. Aiming at a large-scale production of perovskite solar cells, replacement of Pb2+ with a non-toxic element is highly desirable. However, lead-free perovskites have received relatively little attention in the literature if compared to the dominant lead-based systems. Double metal perovskites, in which Pb2+ is replaced by two metallic cations, have been recently proposed as a non-toxic alternative. Substituting lead with two isoelectronic cations opens up the possibility for a large variety of novel perovskites. In view of the possible application of double metal perovskites in the photovoltaic field, a thorough characterization of their optoelectronic properties is required.
Here, we report the time-resolved change in microwave conductance (TRMC) on pulsed illumination in single crystals of a bismuth double perovskite. Due to the high absorption coefficient of the crystal, light-induced charge carriers typically recombine rapidly on a timescale of around 1 ns. Interestingly, on excitation close to the band-gap, the TRMC signal shows a long-lived tail after a rapid initial decay. The presence of a long tail indicates that mobile charge carriers with a remarkably long lifetime of ca. 100 μs are generated in the material. Such a long lifetime is very encouraging for photovoltaic applications of this material. We assign the long lifetime to charge carriers generated in the bulk of the crystal, where they are able to escape surface recombination; we show that by reducing the size of the crystal, and hence reducing the average distance between the photogenerated charges and the crystal surface, charges can no longer escape surface recombination and the long-lived tail is strongly suppressed.
Furthermore, we perform temperature dependent TRMC measurement in single crystals. Most remarkably, the TRMC signal increases upon increasing the temperature. This feature is in contrast to what observed in lead perovskites, and indicates either a thermally activated charge transport or a thermally activated photogeneration. We use pulse-radiolysis time-resolved microwave conductance (PR-TRMC) measurements to determine the charge mobility as a function of temperature, independently of the yield of charge generation. The results allow us to disentangle charge generation and charge transport and to explain the striking temperature dependence observed in the TRMC data.
5:15 PM - ES1.16.04
Consolidation of the Optoelectronic Properties of CH3NH3PbBr3 Perovskite Single Crystals
Bernard Wenger 1 , Pabitra Nayak 1 , Henry Snaith 1 Show Abstract
1 , University of Oxford, Oxford United Kingdom
In polycrystalline lead halide perovskite films, defects are usually most prominent at the surface and at the grain boundaries. Moreover, with diffusion length on the same order of magnitude than the grain size, surface defects are likely to be readily populated and thus the overall properties of the materials will be governed by surface effects. For these reasons, several research groups have proposed to study perovskite single crystals to disentangle the intrinsic properties of the bulk materials from their surface properties. Outstanding properties such as ultra- low defect densities and extremely long carrier lifetimes and diffusion lengths have been reported. However, a large discrepancy in the fundamental optoelectronic properties of single crystals between different reports suggests that the current understanding is still incomplete.
In this work, we synthesize large single crystals of CH3NH3PbBr3 and measure their optical properties using a range of spectroscopic techniques (UV-Vis absorption, optical modeling, steady-state and time-resolved photoluminescence (PL) with 1- and 2-photon excitation). We characterise in the detail the optical absorption and photoluminescence and show that the optical properties of single crystals of CH3NH3PbBr3 are almost identical to the optical properties of polycrystalline thin films. Notably, as judged from both single and two photon PL measurements, we determine the electronic trap density within the single crystals to be very similar to the trap densities in polycrystalline thin films, in the range of 1016 cm-3, in contrast to 109 to 1013 cm-3 as previously estimated for single crystals by electronic methods. Therefore, a critique of our current understanding of the electronic properties of perovskite single crystals is required. Encouragingly, our findings indicate that polycrystalline thin films may already be close to, if not equal to possessing single- crystal-like optoelectronic properties.
5:30 PM - ES1.16.05
Thin-Film Single Crystal Metal-Halide Perovskite for Optoelectronics via Mechanical Spalling Transfer
Sang-Hoon Bae 1 , Jin-wook Lee 1 , Chanyeol Choi 2 , Pengyu Sun 1 , Yunjo Kim 2 , You Seung Rim 1 , Qifeng Han 1 , Jeehwan Kim 2 , Yang Yang 1 Show Abstract
1 , University of California, Los Angeles, Los Angeles, California, United States, 2 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Recently, the hybrid perovskite (PVSK) has been emerging as a promising material for the optoelectronics. Within a few years of development, PVSK solar cells with certified 22% power conversion efficiency (PCE) have been recently achieved. It has to be noted that such a high efficiency has been obtained even with its defective polycrystalline form. This suggests more room for improving efficiency exists if PVSK solar cells can be fabricated in a single-crystalline form as one can expect longer diffusion length and carrier lifetime. In addition, it has been reported that strong below-bandgap absorption could offer for the single-crystalline PVSK which could improve the short circuit current density (Jsc), and eventually increases power conversion efficiency (PCE) of solar cells. However, the growth of single-crystalline PVSK is currently based on the solution methods, such as cooling solution crystallization, inverse temperature crystallization, and antisolvent crystallization, which only produces bulky shape single-crystalline PVSK. Unlike thin film single-crystalline materials, the bulky shape PVSK might have more chance for the charge bulk recombination, which induces the loss of open circuit voltage (Voc) and fill factor (FF). In addition, the bulky single-crystalline PVSK has the disadvantage in terms of material consumption too. Thus, it is hard to expect significant benefits by directly using the bulky single-crystalline PVSK for the solar applications and, thus, another method has been required for single-crystalline PVSKs based solar cells.
We, for the first time, demonstrate a method to form thin film single-crystalline PVSKs by using mechanical spalling methods. Firstly, single-crystalline PVSKs are grown using the solution process. Next, the tensile stress is induced by applying the strained-layer on the top of single-crystalline PVSKs. Modeling result helps us to expect a critical point for stable stress level. A control of the fracture mode makes the bonding inside single-crystalline PVSKs broken along the direction of interface between the strained-layer and single-crystalline PVSKs, which successfully produces thin film single-crystalline PVSKs. In addition, the thickness of thin film single-crystalline PVSK can be controlled via controlling the stress level. Through several measurements, we confirm that the properties of the material do not change even after the spalling process. We believe that this approach can be a useful tool to go beyond the current organic-inorganic hybrid PVSK technology.
5:45 PM - ES1.16.06
Extreme Sensitivity of Optoelectronic Properties of Methylammonium-Lead Tribromide Single Crystals to Environmental Gases
Hong-Hua Fang 1 , Sampson Adjokatse 1 , Haotong Wei 2 , Jie Yang 1 , Graeme Blake 1 , Jinsong Huang 2 , Jacky Even 3 , Maria Antonietta Loi 1 Show Abstract
1 , University of Groningen, Groningen Netherlands, 2 , University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 3 , Université Européenne de Bretagne, Rennes France
In this work, we find that the optoelectronic properties of methylammonium-lead tribromide (MAPbBr3) single crystals exhibit extreme sensitivity to environmental gases. We show evidence that the surface trap state density can be reversibly controlled by the physisorption of oxygen and water molecules, leading to a modulation of the photoluminescence intensity modulation of by over two orders of magnitude. By time resolved single- and two-photon photoluminescence spectra, we demonstrate an unusually low surface recombination velocity (SRV) of 4 cm/s (corresponding to a surface trap state density of 108 cm-2) in MAPbBr3 single crystals. This is the lowest value ever reported for hybrid perovskites, and is 3 orders of magnitude smaller than the one of detector grade silicon crystals. In addition, a modulation of the transport properties in the single crystal devices is presented. Our findings highlight the importance of environmental conditions on the investigation and fabrication of high-quality, perovskite-based devices, and provide a new potential application of these materials for detecting oxygen and water vapor.