5:00 PM - *EP3.2.06
Certified Efficiency of 15.57% in Perovskite Solar Cells with Area > 1cm2
Liyuan Han 1,Wei Chen 2,Yongzhen Wu 1,Xudong Yang 3,Ashraful Islam 1
1 NIMS Tsukuba Japan,2 Huazhong University of Science and Technology Wu Han China3 Shanghai Jiao Tong University Shanghai China
Show AbstractOrganic-inorganic metal halide perovskite solar cells (PSCs) have reached extremely high power conversion efficiency (PCE) of 18~20%. However, all of the high PCEs were achieved by tiny cells (working area
5:30 PM - EP3.2.07
Co-Planar Single-Crystal Hybrid Perovskite Solar Cells
Qingfeng Dong 1,Yanjun Fang 1,Yuchuan Shao 1,Jinsong Huang 1
1 University of Nebraska Lincoln Lincoln United States,
Show AbstractLong, balanced electron and hole diffusion lengths are critical for highly efficient perovskite solar cells. We will report the discovery of the ultra-long diffusion lengths in CH3NH3PbI3 single crystals grown by a solution-growth method. [1] These long diffusion lengths result from greater carrier mobility, longer lifetime, and much smaller trap densities in the single crystals than in polycrystalline thin films. The much longer carrier diffusion lengths in CH3NH3PbI3 single crystals allow the photogenerated charges to be efficiently collected along the lateral direction. We show that perovskite solar cells can be fabricated with a co-planar structure, or lateral structure, or coplanar structure, using CH3NH3PbI3 single crystals which dramatically enhance the device efficiency by 44 times compared with polycrystalline based devices. [2] The lateral structure solar cell eliminates the need for expensive transparent electrodes which potentially largely reduce cost of perovskite solar cell. It also enhances the light harvesting efficiency because of eliminated loss of light by the transparent electrodes through absorption, reflection, and scattering, and allows light trapping using a simple texture structure as established in single-crystal silicon solar cells. The demonstration of efficient lateral-structure perovskite solar cells allows new design of device structures based on perovskite single crystals as well as tandem solar cells by integrating perovskite devices with other types of solar cells.
Reference:
[1] Qingfeng Dong, Yanjun Fang, Yuchuan Shao, Padhraic Mulligan, Jie Qiu, Lei Cao, Jinsong Huang, Electron-hole diffusion lengths > 175 μm in solution-grown CH3NH3PbI3 single crystals. Science, 347(6225), 967-970.
[2] Qingfeng Dong, Jingfeng Song, Yanjun Fang, Yuchuan Shao, Stephen Ducharme and Jinsong Huang, Lateral-Structure Single-Crystal Hybrid Perovskite Solar Cells Through Piezoelectric Poling, Advanced Materials, In Press.
5:45 PM - EP3.2.08
Lead Acetate Based Perovskite Hybrid Solar Cells with Very Low Hysteresis and High Efficiency
Trilok Singh 1,Tsutomu Miyasaka 1,Ajay Jena 1
1 Graduate School of Engineering, Toin University of Yokohama Toin University of Yokohama Yokohama Japan,
Show AbstractThe organic-inorganic perovskite structured semiconductors (CH3NH3PbX3, X= Br, Cl, I) have gained a lot of attention as light harvesters in thin film photovoltaic cells (PVCs) due to their unique light absorption, charge carrier transport properties and low cost. In last five years the power conversion efficiency has exceeds 20%, however there is still a huge possibility of improvement to reach near the theoretical limit (31%). Furthermore, in order to optimize device performance and long term stability, better understanding of the general working principle of these optoelectronic devices with respect to various permutation and combination are needed. There have been a plenty of literature on the fabrication of organic–inorganic metal halide perovskite thin films with most of the processes limited to halide based anions as starting materials.
The present talk will focus on the role of the anions in the perovskite solution and their influence in particular, perovskite crystal growth, film formation, device performance and stability on perovskite solar cells grown in N2 filled glovebox as well as in humidity controlled conditions. Our recent finding showed that a non-halide lead source (lead acetate) instead of lead chloride or iodide, the perovskite crystal growth is much faster and resultant films are very smooth. Further the systematic modifications of fabrication process led high efficiency (> 18.5%) with high open circuit voltage (Voc= 1.08 V) and very low hysteresis. We observed that stability is not only strongly affected by ambient conditions, but also by the lead precursor employed for the perovskite deposition. The results highlight that other lead sources are also suitable for the development of PSCs, opening a new possibilities for device performance optimization.
EP3.3: Poster Session I
Session Chairs
Wednesday AM, March 30, 2016
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - EP3.3.01
Carbazole-Based Hole-Transporting Materials for Perovskite Solar Cells: Increasing Stability and Performance
Jonathan Tinkham 1,Alan Sellinger 1
1 Colorado School of Mines Golden United States,
Show AbstractPerovskites are an attractive class of materials for use in photovoltaic devices, but there remain challenges preventing deeper understanding and wider adoption. Devices need an interfacing hole-transporting material (HTM) to extract holes, and a single material (spiro-OMeTAD) is currently dominant, but is expensive and difficult to use. The perovskite layer is also sensitive to water, with hydration resulting in low device lifetimes. There are also significant losses (~0.2 eV) from hole-extraction due to large band offsets, and recombination from trap-sites at the perovskite-HTM interface and in the HTM itself.
Carbazole-based small-molecule derivatives are being prepared to address and study these issues. Larger alkyl chains have increased hydrophobicity and this has increased device lifetimes through the exclusion of water. Oxidized salts of the HTM are also being investigated as alternative dopants in order to remove LiTFSI, and this process has also resulted in increased hydrophobicity and stability. This has been further expanded upon by selective fluorination, which also grants a 0.1 eV reduction in EHOMO in addition to increased hydrophobicity. These fluorinated materials are the first few entries in a series of molecules that posses decreasing EHOMO and increasing Voc. Other members of this series include pyridine incorporating derivatives that should also obviate the need for Lewis-basic additives to passivate the perovskite surface to reduce recombination.
The harmonization of these improvements will allow the synthesis of a single-component HTM that will simplify preparation of devices, driving down cost and increasing adoption, along with improvements in performance and lifetime.
9:00 PM - EP3.3.02
Highly Luminescence Colloidal Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X=Cl, Br, and I): The Path from Synthetic Methodologies to Lasing Studies
Loredana Protesescu 2,Sergii Yakunin 2,Georgian Nedelcu 2,Maksym Kovalenko 2
1 ETH Zurich Zurich Switzerland,2 and Empa-Swiss Federal Laboratories for Materials Science and Technology Dubendorf Switzerland,
Show AbstractChemically synthesized inorganic nanocrystals (NCs) are considered to be promising building blocks for a broad spectrum of applications including electronic, thermoelectric, and photovoltaic devices. Using inexpensive commercial precursors, we have synthesized fully inorganic cesium lead halide perovskites (CsPbX3, X=Cl, Br, and I or mixed halide systems Cl/Br and Br/I) in the form of monodisperse colloidal nanocubes (4-15 nm edge lengths) [1]. Through compositional modulations and quantum size-effects, their bandgap energies and emission spectra are readily tunable over the entire visible spectral region of 410-700 nm. The photoluminescence of CsPbX3 NCs is characterized by narrow emission line-widths of 12-42 nm, wide color gamut covering up to 140% of the NTSC color standard, high quantum yields of up to 90% and radiative lifetimes in the range of 4-29 ns. Particularly appealing from those series of materials are highly-stable blue and green emitting CsPbX3 NCs (440-530 nm), since the corresponding metal-chalcogenide QDs show reduced chemical and photo-stability at these wavelengths [1].
Post-synthetic chemical transformations of colloidal NCs, such as ion-exchange reactions, provide an avenue to compositional fine tuning or to otherwise inaccessible materials and morphologies. While cation-exchange is facile and commonplace, anion-exchange reactions have not received substantial deployment. Furthermore, fast inter-nanocrystal anion-exchange is demonstrated, leading to uniform CsPb(Cl/Br)3 or CsPb(Br/I)3 compositions simply by mixing CsPbCl3, CsPbBr3 and CsPbI3 nanocrystals in appropriate ratios [2].
Inspired by the highly efficient photoluminescence, we tested CsPbX3 NCs as inexpensive optical gain medium. We observed that room-temperature ultralow-threshold amplified spontaneous emission (ASE) can be obtained in the whole visible spectral range (440-700 nm) with low pump thresholds down to 5±1 μJ cm-2 and high values of modal net gain of at least 450±30 cm-1 while films of CsPbX3 microcrystals possess at least order of magnitude higher ASE thresholds. Two kinds of lasing modes are successfully realized: whispering gallery mode lasing using silica microspheres as high-finesse resonators, conformally coated with CsPbX3 NCs, and random lasing in films of CsPbX3 NCs [3].
[1] Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. Nano Letters 2015, 15, 3692.
[2] Nedelcu, G.; Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Grotevent, M. J.; Kovalenko, M. V. Nano Letters 2015, 15, 5635.
[3] Yakunin, S.; Protesescu, L.; Krieg, F.; Bodnarchuk, M. I.; Nedelcu, G.; Humer, M.; De Luca, G.; Fiebig, M.; Heiss, W.; Kovalenko, M. V. Nat. Commun.,2015, 6:8056 doi: 10.1038/ncomms9056
9:00 PM - EP3.3.03
Ions and Defects Migration in Hybrid Perovskite CH3NH3PbI3
Yecheng Zhou 1,Angus Gray-Weale 1
1 The University of Melbourne Melbourne Australia,
Show AbstractPhotovoltaic cells with absorbing layers of certain perovskites have power conversion efficiencies up to 20%. High performances, slow photovoltaic responses and anomalous hysteresises in perovskite solar cells have drawn lots of attention. Among these perovskite materials, CH3NH3PbI3 is widely used. Anomalous hysteresis has caused much debate. Most of experimentalists and theoreticians believe that the reason for slow photovoltaic responses and anomalous hysteresis effects is ions migration. However, the slow photovoltaic responses experiment done by Gottesman et al. cannot be explained with ions migration.
Theoretically, we shown that polarisation is a possible reason for high performance and hysteresis. But we have no reason to deny the argument that it is possible for ions to migrate inducing hysteresis effects. If the slow response screen field in numerical simulations comes from ion migration, it also makes sense. Therefore, we are going to study ions and defects migration and polarisation relaxation behaviors in CH3NH3PbI3. First principle studies already shown that the energy barriers for defects migrations are from 0.08 eV to 0.40 eV, which depend on the ions types. While the energy barrier for MA+ reorientation is about 0.01 eV to 0.10 eV, which depend on the initial and final MA+ orientations and the orientations of neighbor MA+ orientation. From the base of energy landscape, polarisation responds more easily and screens the external field. Considering screening effect is a collective behavior, the relaxation behavior is totally different to individual polar or defect movement. Additionally, to determine which one dominates the screening and hysteresis effect in perovskite solar cells, a multi-scale polarization and defects relaxation numerical model is developed.
Our viewpoint is that polarisation does induce slow photovoltaic responses and anomalous hysteresis effects. With Density Functional Theory (DFT) calculations, we have shown that methylammonium ions (MA+) in CH3NH3PbI3 prefer to rotate collectively, and to be parallel to their neighbors. This collective rotation and orientation contributes to polarisation of perovskite. The field induced by this polarisation is strong enough to screen the hindering field, and then promote charge transfer and improve solar cells’ performance. This screening field agrees with the compensated field observed in experiments. A numerical model for perovskite solar cells was developed to discuss how the polarisation and capacitive charges affect its performance. Our numerical model verified the improvement mechanism. Additionally, by implementing the relaxation of polarisation and capacitive charges into numerical model, it reproduced rate dependent normal and anomalous hysteresis I-V curves.
9:00 PM - EP3.3.04
Efficient Planar Heterojunction Perovskite Solar Cells Fabricated by Bar Coating
Xuan Liu 1,Liyan Yang 1,Yu Yang 1,Tao Wang 1
1 Wuhan Univ of Technology Wuhan China,
Show AbstractOrganohalide lead perovskite solar cells with the light absorbing layer cast from solutions have achieved a high efficiency over 20% within the past five years. It is known that the nano- and meso- scale morphology of the active layer plays a critical role on the highest efficiency a device can achieve, as well as the reproducibility of efficiencies. The morphology developed in the film casting process depends on the casting methods, the environment, the materials as well as the solutions. We have fabricated the perovskite layer of this type of solar cells by bar coating, a process that is capatible with large scale device fabrication. The nanostructure formed during the bar coating process and its correlation with device performance is discussed.
9:00 PM - EP3.3.05
Room Temperature Fabrication of CH3NH3PbBr3 by Anti-Solvent Assisted Crystallization Approach for High Performance Bromide-Based Perovsktie Solar Cells
Xiaojia Zheng 1,Bo Chen 1,Congcong Wu 1,Shashank Priya 1
1 Virginia Tech Blacksburg United States,
Show AbstractCrystallization is a widely used technique in solid–liquid separation processes. In past two decades, adding a secondary solvent known as anti-solvent (a liquid in which the solute is insoluble) to the solution to reduce the solubility of the solute and consequently to generate a supersaturated driving force, has been drawing much attention. Both the crystal structure and morphology can be modulated conveniently through the control of anti-solvent composition, addition rate and initial concentration during the synthesis process, which enables the fabrication of high quality, homogeneous and pinhole-free films at low temperatures. Reducing the temperature of synthesis reduces the risk of forming structural, ionic and charged defects. CH3NH3PbBr3 perovskite, with a bandgap of ~2.3eV and can be further modulated to achieve a lower value by doping with iodide, which can provide a considerably higher Voc. High Voc is beneficial towards using as the front cell in multijunction solar cells or driving the electrochemical reactions smoothly to open new applications. Moreover, CH3NH3PbBr3 perovskite shows a better stability than the CH3NH3PbI3 perovskite. In this work, we use anti-solvents assisted crystallization (ASAC) approach to modulate the microstructures of CH3NH3PbBr3. Our room temperature ASAC approach can avoid the post-annealing process, which minimizes the formation of surface electron traps and corresponding slow transient current. Compared to the conventional spin-coating process, this ASAC approach can improve the Voc from 1.01V to 1.42V and PCE from 3.15% to 8.29%. More importantly, the devices obtained by ASAC show fast photocurrent response and small J-V hysteresis benefiting from the excellent electronic and optoelectronic properties of the CH3NH3PbBr3 thin film. This is one of the highest efficiency reported in CH3NH3PbBr3 solar cells and shows the tremendous progress compared to the conventional spin-coating process.
9:00 PM - EP3.3.06
Interfaces in Graphene-Organolead Halide Nanohybrid Perovskite Solar Cells Examined by In Situ Spectroscopy
Muge Acik 1,Marjorie Segovia 2,Seth Darling 3
1 Center for Nanoscale Materials Argonne National Laboratory Lemont United States,2 Department of Chemistry University of Chile Santiago Chile1 Center for Nanoscale Materials Argonne National Laboratory Lemont United States,3 Institute for Molecular Engineering University of Chicago Chicago United States
Show AbstractPerovskite solar cell (PSC) power conversion efficiency (PCE) has improved to ≥20%. Among PSCs, organolead halide perovskites have stood out with their long electron-hole diffusion length, efficient light absorption, and high electron/hole mobility.
While PCEs have skyrocketed, there is insufficient understanding of the underlying optoelectronic function in these devices. Interfaces, in particular, play a central role in the function of many types of solar cells. In this context, interfaces are hosts for charge trapping sites such as defects in the graphene-related layered nanohybrids (GLN). We study perovskite interfaces with n-type electron (ETL) or p-type hole transport layers (HTL) and in the presence of scaffold media (Al2O3, TiO2, etc.) using GLNs (graphene oxide, reduced graphene oxide, n-doped graphene) as ETL and HTL. Preferential interactions of layers with precursor materials, charge extraction and recombination at the interfaces, interfacial design and controlled perovskite film growth are explored for controlled grains and self-passivation of the defect states to enable low-cost devices.
To understand interfacial working mechanisms of PSCs and perovskite film formation mechanisms, we perform variable temperature (-195°C to 600°C) in situ infrared absorption spectroscopy and in situ micro Raman spectroscopy. We perform semi-quantitative spectroscopic analysis derived from the intensity and peak areas of vibrational normal modes of C-H (~2800-3200 cm-1) and N-H (~2000-2800 cm-1) moieties in the presence of organolead halides (CH3NH3PbI3, CH3NH3PbBr3, and CH3NH3PbCl3) and their interfacial reactions with oxygen functional groups (ethers, hydroxyls, carboxyls, carbonyls, epoxides, etc.) of GLNs. Effect of halides on the final film morphology is monitored as a function of annealing temperature. Raman analysis also provides defect analysis with ID/IG ratio variation at perovskite/GNL interfaces at low and high temperature treatments.
9:00 PM - EP3.3.07
Chemical Kinetics Understanding of CH3NH3PbI3 Formation from Controlled Solid-Gas Reaction Approach
Jian Mao 1,Hong Zhang 1,Hexiang He 2,Haifei Lu 1,Fengxian Xie 1,Di Zhang 1,Kam Wong 2,Wallace Choy 1
1 Electrical and Electronic Engieering The University of Hong Kong Hong Kong China,2 Department of Physics The Hong Kong University of Science amp; Technology Hong Kong China
Show AbstractOrganic-inorganic perovskite, ABX3 (A = CH3NH3 or HC(NH2)2, B = Pb or Sn, and X = Cl, Br, or I), solar cell has attracted global attention for its high power conversion efficiency (PCE of 20.1%), facile preparation, and potential low cost. It is generally accepted that the PCE of perovskite solar cell is significantly dependent on the morphology of perovskite thin film, which is strongly affected by the reaction between metal halide and organic halide. Compared with strong ionic interaction between metal cation and halide cation in solvent, the reaction between solid metal halide and gaseous organic halide is much slower and controllable. However, the chemical kinetics of perovskite from solid-gas reaction is rarely reported, which is important for understanding of perovskite formation and decomposition. Herein, we combine the theoretic kinetic analysis and experimental results to investigate the formation of perovskite from solid-gas reaction approach. According to the Rate law and Arrhenius equation, the reaction rate between solid PbI2 and gaseous CH3NH3I is a function of temperature and these two compounds’ concentration. In experiment, we found that the reaction rate between them at room temperature is so slow that large amount of raw PbI2 was detected by XRD after formation. However, after increasing the temperature to 50°C, 60 °C, and 70 °C, the reaction rate was quite improved and no residual PbI2 was measured. Besides, the concentration of CH3NH3I was controlled via tuning its evaporation rate (0.5 Å/s, 0.9 Å/s, and 1.3 Å/s). Lower concentration lead to slower reaction rate between PbI2 and CH3NH3I, smaller crystal size of perovskite, and smoother morphology (Rq=7.37 nm). With about 250 nm perovskite active layer, the solar cells with structure of ITO/PEDOT:PSS/perovskite/PCBM/PFN/Ag exhibits a PCE of 10.0% (Jsc = 14.65 mA/cm2, Voc = 0.93 V, FF = 0.73) with little hysteresis.
9:00 PM - EP3.3.08
Lead Halide Perovskite/Polymer Composite Material for Improved Moisture Stability: Synthesis and Characterization
John Murphy 1,Jessica Andriolo 1,Brandon Ross 1,Jack Skinner 1
1 Montana Tech of the University of Montana Butte United States,
Show AbstractOrganic-Inorganic perovskites (OIPs) have generated a great deal of interest in recent years due to their rapid ascent in power-conversion efficiencies. However, moisture-driven decomposition of OIPs remains an obstacle to their ultimate potential in the photovoltaic industry. Several approaches have been taken to mitigate OIP exposure to moisture. These approaches have focused on manipulation of OIP synthesis as well as the introduction of a protective environment in which the OIP can exist while maintaining photovoltaic properties. Both approaches have been implemented using traditional solution-based processing techniques. This research proposes a solution-less synthesis method of OIPs in which a composite structure of OIP in protective polymer matrix is produced. The proposed method simultaneously passivates OIP structures while the growth of OIP crystals occurs. We have demonstrated growth of lead halide perovskite in a poly(propylene) matrix, characterized using XRD and SEM/EDS. To further demonstrate the potential of OIPs synthesized in polymer, we are tracking the course of moisture-driven decomposition. In this research, samples are maintained in ambient conditions with humidity monitoring and characterized every 24 hours to track degradation of lead halide perovskites. Synthesis of OIP within a polymer matrix should provide an alternative synthesis method which enhances stability of perovskite crystals, and in turn, improves their utilization in the solar energy industry.
9:00 PM - EP3.3.09
Effects of TiO2 Properties on the Performance of a CH3NH3PbI3 Perovskite Photovoltaic Cell
Hasyiya Adli 1,Takashi Harada 1,Shuji Hozan 1,Seigo Ito 2,Shuji Nakanishi 1,Shigeru ikeda 1
1 Research Center for Solar Energy Chemistry Osaka University Osaka Japan,2 Department of Electric Engineering and Computer Science, Graduate School of Engineering University of Hyogo Hyogo Japan
Show AbstractRecently, organic-inorganic solar cells based on trihalide perovskites of the CH3NH3PbX3 (X= I−, Br−, Cl−) family have been gaining tremendous attention due to their cost effectiveness, ease of fabrication, and superb photovoltaic performances.1 The first perovskite solar cell (PSC) was reported in 2009 using an electrolyte as a hole transporting material2 following subsequent improvement with PCEs rising from 3.8% to 20.1% within five years. In this study, TiO2 is used as a middle layer between perovskite and transparent conductive oxide (TCO) layers. Despite many reports of excellent PCEs, only few studies in which the effects of physical and chemical structures of TiO2 on solar cell performance were investigated systematically.3,4 Therefore, in this study, we carefully investigated the effects of porosity and amounts of OH groups in the porous TiO2 (pTiO2) layer on the photovoltaic performance in relation to structures of CH3NH3PbI3 perovskite. By changing the heat treatment temperature (TpTO) during the fabrication of pTiO2 from 400 °C to 700 °C, its porosity and its amount of surface OH groups were varied without alteration of the crystalline structure (anatase). PCEs of solar cells at different TpTO showed a volcanic-like pattern depending on TpTO of pTiO2; the highest PCE was obtained by using pTiO2 prepared at TpTO of 550 °C. Structural analysis of CH3NH3PbI3 perovskite part indicated that at relatively low TpTO (< 550 °C) formation of CH3NH3PbI3 perovskite was inhibited by the presence of a large amount of surface OH groups on pTiO2. Meanwhile, at relatively high TpTO surface OH groups were decreased with increase in TpTO, and significant reduction of porosity of pTiO2 was also occurred due to extinction of meso and micro pores and sintering between TiO2 particles. This structural alteration hindered the penetration of CH3NH3I into the pore channel of TiO2 filled with PbI2, resulting in a large amount of PbI2 remained in the finally obtained photovoltaic cell. Hence, these PbI2 layers suppressed electron transfer from CH3NH3PbI3 to TiO2, inducing a decrease in JSCs and PCEs. In conclusion, the optimum TpTO (550 °C) for fabrication of pTiO2 should be determined by its porous nature and sufficient removal of surface OH groups.
Reference
1) Snaith, H. J., J. Phys. Chem. Lett. 2013, 4, 3623.
2) Kojima, A. et al., J. Am. Chem. Soc. 2009, 131, 6050.
3) Murugadoss, G. et al., APL Materials 2014, 2, 081511-1.
4) Dharani, S. et al., Nanoscale 2014, 6, 1675.
9:00 PM - EP3.3.10
Role of Thin MgO Layer in Suppressing Interfacial Recombination Loss at FTO-TiO2 Interface in Perovskite Solar Cells
Ashish Kulkarni 1,Ajay Jena 1,Masashi Ikegami 1,Tsutomu Miyasaka 1
1 Toin Univ of Yokohama Tokyo Japan,
Show AbstractIn the recent years, perovskite solar cells have gained huge attention because of the sky-rocketing rise in their power conversion efficiency. In the structure of these perovskite devices, an electron collecting/hole blocking layer plays an important role for efficient carrier collection. A thin compact layer of TiO2 is being widely used as an electron collecting/hole blocking layer in both the planar and meso-structure perovskite solar cells. This dense layer of TiO2 deposited on FTO substrates is believed to reduce recombination by preventing direct contact between FTO and perovskite or hole transporting material and thereby, improve the open circuit voltage (Voc). On the contrary, we found that there is a reasonable loss in open circuit voltage (Voc) in TiO2 mesoscopic perovskite (CH3NH3PbI3) solar cells due to recombination caused by TiO2 compact layer at its interface with the FTO substrate. A thin layer of MgO in place of TiO2 compact layer (50-60 nm), therefore, enhanced Voc of the cell significantly (from 0.86 V to 0.98 V) while the MgO layer coated on TiO2 compact layer (TiO2-MgO bilayer) does not change the Voc much (from 0.86 V to 0.90 V). However, photocurrent density (Jsc) increased in the case of TiO2-MgO bilayer, which resulted in improvement of overall cell efficiency (~12%). In addition, it was interesting to find that the devices with and without TiO2 compact layer showed similar Voc (~0.86 V). This indicated that the layer of TiO2 may not necessarily influence Voc in a TiO2 mesoscopic perovskite cell fabricated by two step method as the residual PbI2 acts as a passivation layer on FTO and prevents direct contact of perovskite with the substrate. Hence, the choice of material to be used as hole blocking/electron collecting layer becomes important for improving the cell efficiency.
9:00 PM - EP3.3.11
Efficient Spray and Brush Fabrication Methods for Perovskite Solar Cells
Ashwith Kumar Chilvery 1,Anderson Sunda-Meya 1,Morewell Gasseller 1
1 Xavier Univ of Louisiana New Orleans United States,
Show AbstractPerovskite compounds have the potential to transform photovoltaic as they are easy to fabricate, have better stability, and posess superior power conversion efficiency. In this research, a versatile solution-processing method namely “Spray+Brush” has been adopted to achieve a power-conversion efficiency of 3.52% for pure organo-metal halide perovskite devices. It has been observed that this novel method is more efficient and cost-effective than the perovskite devices fabricated by spray (1.95%) and brush (1.17%) methods alone. The Spray+Brush method of solution processing can be promising for various other organic coatings and other flexible devices.
9:00 PM - EP3.3.13
Influence of Temperature-Dependent Phase Transition on Amplified Spontaneous Emission of Waveguides Based on Solution-Processed Perovskite Films
Liang Qin 1,Longfeng Lv 1,Yanbing Hou 1
1 The Beijing Jiaotong University Beijing China,
Show AbstractOrganic-inorganic halide perovskites have recently attracted tremendous attention to photovoltaic applications, light-emitting diode and lasing device due to its high gain coefficient, low lasing threshold, high mobility, wide wavelength range and high photochemical stability. Some work revealed that the CH3NH3PbX3 (X=Cl, Br, I) crystals undergoes two or three phase transitions at different temperatures. In this work, we investigated the cryogenic photoluminescence and absorption of a CH3NH3PbI3 perovskite film. The results show that an exciton binding energy of 65±3meV via one-step method and 67±6 meV via two-step method and both have abnormal spectra-shift along with different temperature. The amplified spontaneous emission of perovskite waveguides at different temperature shows a low-threshold lasing behavior at the phase transition. Our results would be beneficial to enhanced understanding in the unique properties of hybrid perovskite materials and provided an effective strategy for achieving an efficient electric-pumped lasing device.
9:00 PM - EP3.3.14
An Hydrophilic Anode Interlayer for Solution Processed Organohalide Perovskite Solar Cell
Qianqian Lin 1,Dani Stoltzfus 1,Ardalan Armin 1,Paul Burn 1,Paul Meredith 1
1 Univ of Queensland Brisbane Australia,
Show AbstractEngineering the active layer-electrode interfaces is a key task in optimising thin film inorganic, nano-crystal, and organic semiconductor optoelectronic devices.[1] In the context of solar cells, modification of the electrode surface and/or the introduction of interlayers between the electrode and active layer can enable tuning of the electrode work function, control over the carrier separation and collection, and the minimization of carrier trapping and accumulation.[2] Recently, organohalide perovskite solar cells (PVSCs) have emerged as a high efficiency and potentially low cost next generation photovoltaic technology.[3] It has been recognised that tuning the ionisation potential and electron affinity of the interlayers between the active layer and the electrodes can lead to an improved Voc.[4]
With the focus on solution processing for large area PVSCs, solving the ionisation potential-film quality issue is important. Attaining the desired organohalide perovskite film essentially boils down to matching the surfaces energies of the deposition surface (electrode interlayer) and the evolving film after casting. In our experience, other organic semiconductors, including those previously used in physical vapour deposited PVSCs[4], are unsuitable for solution processing due to the mismatch in surface energies.Therefore, it is critical to develop interlayers that can meet three requirements: (i) have an appropriate ionization potential to match the valence band energy of the chosen organohalide perovskite; (ii) provide a suitable surface energy to allow for high quality polycrystalline film formation using solution processing methods; and (iii) not be soluble in the solvent used to deposit the organohalide perovskite precursors. To date these requirements are yet to be achieved in an interlayer and are the motivation for the work we report here.
In this work, we utilize a sulfonium precursor polymer poly(1,4-phenylenevinylene) (PPV) as a method of forming an ultra-thin p-type interlayer with the required surface energy for high quality organohalide lead perovskite film formation via solution processing, while at the same time a having a large enough ionization potential.[5] We thus obtain open circuit voltages as high as those obtained in evaporated PVSCs ~1.06 V and clearly demonstrate the principle of work function and Voc tuning in simple, non-oxide containing planar homojunctions. The optimized devices have a power conversion efficiency of ~15% with minimized charge carrier recombination.
References:
[1] M. Grätzel et al. Nature, 488, 304-312 (2012).
[2] H.-L. Yip et al. Energy Environ. Sci. 5, 5994-6011 (2012,).
[3] N.J. Jeon et al. Nature, 517, 476-480 (2015).
[4] Q. Lin et al. Nature Photon. 9, 106-112 (2015).
[5] Q. Lin et al. Adv. Mater.Interfaces, DOI: 10.1002/admi.201500420 (2015).
9:00 PM - EP3.3.15
Promising Interface Modification of Nanostructured TiO2/CH3NH3PbI3 Heterojunction to Enhance Solar Cell Performance
Yen-Chen Shih 1,Lee-Yih Wang 3,King-Fu Lin 2
1 Materials Science and Engineering National Taiwan University Taipei Taiwan,2 Institute of Polymer Science and Engineering National Taiwan University Taipei Taiwan,3 Center for Condensed Matter Sciences National Taiwan University Taipei Taiwan1 Materials Science and Engineering National Taiwan University Taipei Taiwan,2 Institute of Polymer Science and Engineering National Taiwan University Taipei Taiwan
Show AbstractRecently, organometal halide perovskite solar cells have attracted much attention due to their high power conversion efficiency and potentially low cost for manufacturing. However, the incomplete pore-filling of porous TiO2 with perovskite that decrease the performance and reproducibility of devices was the major concern with this photovoltaic device. In this research, several amino acids were applied to modify the TiO2/CH3NH3PbI3 heterojunction interface for reducing the inevitable defects formed during crystallization of perovskite. The power conversion efficiency of the resulting perovskite solar cell was increased from 10.72 to 14.00 % through the α-alanine modification, attributed to the enhancement of the short-circuit current density (from 16.92 to 21.94 mA/cm2). With this promising modification, higher coverage of the CH3NH3PbI3 crystals on the TiO2 surface was obtained, resulting in more efficient charge transfer and higher photocurrent. Based on our results, we believe that this modification has created a new breakthrough for the research of perovskite solar cells.
9:00 PM - EP3.3.16
Performance Variations of Square-Centimetre Planar Mixed-Halide Perovskite Solar Cells Based on Humidity during Synthesis
Harry Cronin 2,K. D. G. Imalka Jayawardena 1,Zlatka Stoeva 2,Maxim Shkunov 1,S. Ravi Silva 1
1 Advanced Technology Institute University of Surrey Guildford United Kingdom,2 DZP Technologies Ltd. Cambridge United Kingdom,1 Advanced Technology Institute University of Surrey Guildford United Kingdom2 DZP Technologies Ltd. Cambridge United Kingdom
Show AbstractPerovskite solar cells (PSCs) are a promising renewable energy technology, but with a number of problems to be overcome before transfer to volume production. One major issue is the sensitive nature of the films to atmospheric conditions under which they are processed. It is well-known that PSCs degrade on storage in humid atmospheres; however, it is now becoming clear that the humidity under which the cells are produced also plays a role in determining structure and thus performance.
In a popular method for producing mixed halide PSCs, PbCl2 and CH3NH3I (MAI) are deposited from a common solvent and annealed for up to two hours. This introduces large scope for variations due to prevailing conditions at the time of annealing – which is exacerbated for large area films in which good surface coverage of the Perovskite layer is essential. In this work, mixed halide MAPbI3-xClx Perovskite solar cells of active area ≈1 cm2 were produced using a standard planar architecture, annealed at 100oC under a range of conditions and characterised electrically, structurally and chemically. Devices produced entirely in the glovebox (0% RH) were poor, while low humidity (around 20% RH) led to the best-performing devices, with the most uniform surface coverage. During annealing at higher humidity (up to 40% RH) the Perovskite films degrade, leading to higher leakage currents and lower VOC. The effect of annealing time was also studied. At low humidity, performance depends only weakly on annealing time, but at high humidity it is very sensitive, supporting the hypothesis that the devices degrade more quickly when exposed to more humidity.
The results point to an optimum humidity level for synthesis, and suggest that the optimum annealing time and humidity are interrelated. A hypothesis for the formation of the material and its subsequent performance is proposed, based on a trade-off between four competing mechanisms. We observe high humidity during annealing to lead to both faster conversion to Perovskite [1] and moisture-assisted grain growth [2], which may aid performance, but this must be balanced by increasing voids [3] and increased film degradation [4]. With knowledge of these trade-offs, we propose a solution to reduce the annealing time necessary to form mixed-halide PSCs by introducing controlled amounts of moisture, thus aiding the future transfer to high volume production.
[1] G. E. Eperon, H. J. Snaith et al., ACS Nano, vol. 9, no. 9, pp. 9380–9393, Aug. 2015.
[2] J. You, Y. (Michael) Yang et al., Appl. Phys. Lett., vol. 105, p. 183902, 2014.
[3] X. Gong, L.-S. Liao et al., Adv. Funct. Mater., Accepted Manuscript, 2015.
[4] J. Yang, T. L. Kelly et al., ACS Nano, vol. 9, no. 2, pp. 1955–1963, 2015.
9:00 PM - EP3.3.17
The Role of Electrostatics and Avalanche Breakthrough in J-V Hysteresis Observed in Methylammonium Lead Halide Perovskite Films
Martina Stumpp 1,Raffael Ruess 1,Jonas Horn 1,Jan Tinz 1,Christoph Richter 1,Derck Schlettwein 1
1 Univ Giessen Giessen Germany,
Show AbstractThe use of methylammonium lead halide materials such as CH3NH3PbI3 and its derivatives in next-generation solar devices is very promising due to the materials' excellent light absorption, low non-radiative carrier recombination and high carrier mobilities. Even though there have been recent studies approaching stable I-V characteristics of perovskite films [1], hysteresis in the current-voltage curves is still often observed, affecting the applicability in solar cells and deserves detailed investigation [2]. Here, J-V hysteresis of methyl ammonium lead halide materials CH3NH3PbI3 and CH3NH3Pb(I0.95Br0.05)3 prepared via different established deposition techniques was studied in a symmetric contact geometry of microstructured gold electrode arrays on Si/SiO2 wafers [3]. Significant changes in the observed current density and residual current at zero applied bias were observed following positive or negative poling showing persistent polarization of the perovskite films. At higher bias voltages additional inverted hysteresis loops were measured pointing at a decrease in barrier width and/or a reduction of the barrier height at blocking perovskite/metal contacts by migrating iodide ions. The net J-V characteristics in this voltage range are, hence, characteristic of two diodes operated back-to-back. Time-dependent studies were performed to analyze the decay of the different observed polarization phenomena in the films during either short-circuit or continuous sweeping of the bias. Implications of such persistent polarization and modification of barriers for technical applications of the materials are discussed.
[1] S. Dharani, H.A. Dewi, R.R. Prabhakar, T. Baikie, C. Shi, D. Yonghua, N. Mathews, P.P. Boix and S.G. Mhaisalkar, Nanoscale 6, 13854 (2014); [2] H.J. Snaith, A. Abate, J.M. Ball, G.E. Eperon, T. Leijtens, N.K. Noel, S.D. Stranks, J.T.-W. Wang, K. Wojciechowski and W. Zhang, J. Phys. Chem. Lett. 5, 1511 (2014); [3] M. Stumpp, R. Ruess, J. Horn, J. Tinz, C. Richter and D. Schlettwein, Phys. Status Solidi A 213, 38 (2016).
9:00 PM - EP3.3.18
Inorganic-Organic Hybrid Perovskite Based Photodiodes with a Transparent Electrode
Rahim Abdur 1,Md Abdul Kuddus Sheikh 1,Son Singh 1,Daekyun Jeong 1,Jaegab Lee 1
1 School of Advanced Materials Engineering Kookmin University Seoul Korea (the Republic of),
Show AbstractMethyl Ammonium Lead Halides, perovskites, have high carrier mobility and high photo conversion efficiency. For these reasons it has become one of the attractive light harvesting semiconducting materials recently. In addition, these materials have advantage of low temperature processing, easy to deposit, large scale processing. Furthermore, the perovskite materials are sensitive to a wide band wavelength from ultraviolet to visible range but inactive in IR region. However, the mechanism for the growth of the hybrid perovskite crystalline structure is not properly understood on the planar surfaces.
In this study, the methyl ammonium lead Iodide was investigated to reveal the effects of the experimental variables such as post anneal temp, post anneal time, and lead iodide-methyl ammonium iodide composition on the growth and the morphology using in situ XRD technique and FE-SEM. Different deposition process were compared to apply perovskite films on planar substrates.
Optimized perovskite films were used to fabricate photodiodes with various structures. Finally we have applied the triple layer transparent electrodes to the photodiodes, which leads opportunity of both side exposure.
9:00 PM - EP3.3.19
High-Throughput Calculations to Optimize Properties and Interfacial Chemistry of Piezoelectric Materials
Jordan Barr 1,Michael Ashton 2,Fang-Yin Lin 2,Susan Sinnott 1
1 Pennsylvania State University University Park United States,2 University of Florida Gainesville United States
Show AbstractPiezoelectrics are well studied and are ubiquitous in today’s electronic devices. Some of the best performing materials, such as Pb(Zr,Ti)O3 (PZT), contain toxic materials and the formation of undesirable secondary phases with metal electrodes is a processing challenge. The aim of this work is to identify potential piezoelectric perovskite materials with the same high performance as PZT without the toxicity and undesirable interfacial chemistry using high-throughput density functional calculations. First, database analysis of the Materials Project was conducted to search for A-B sites that do not form compounds with platinum. This created a list of 1,572 perovskites for further study. Next, the bandgaps of these materials was calculated and a previously determined criterion of a calculated bandgap of 0.25 eV or higher was applied. This reduced the list of potential replacement materials for PZT to 45. Third, the stabilities of these compounds were determined by calculating the energy difference between the given material and its most stable phase, which is referred to as the distance from the hull. This allowed us to compare the 45 compounds to already synthesized materials. The criterion for this calculation was a difference in energy of 100 meV/atom or lower, which further reduced the list down to 15 potential candidates. Next, calculations were carried out to examine the solution energy of alloying the A-B sites in the ABO3 perovskite piezoelectric candidate materials with Pt to identify the materials most resistant to the undesirable secondary phase formation. The results are compared to experimental findings from the literature and from experimental collaborators.
9:00 PM - EP3.3.20
The Growth of the CH3NH3PbCl3 Films and Its Application in Visible Blind Ultraviolet Photodetector
Wenzhen Wang 1,Haitao Xu 1,Yanglin Wu 1,Run Xu 1,Linjun Wang 1
1 School of Materials Science and Engineering, Shanghai University Shanghai China,
Show AbstractThe rapid development of organometallic lead halide perovskite solar cell (MAPbX3, MA= CH3NH3+, X=I-, Br-, Cl-) attract more and more attention due to excellent optoelectronic properties, such as long carrier lifetime, high carrier mobility, strong absorption in the whole visible range. Despite most work regarding the MAPbI3 and MAPbBr3 film for the application of solar cell device, the visible light detector based on MAPbX3 has also been studied by several research groups. [1,2] However, among all three MAPbX3 materials, MAPbCl3 are seldom studied. [3] Very recently, Maculan et al, by the first time, studied the visible blind ultraviolet (UV) detector based MAPbCl3 single crystal grown by the inverse temperature crystallization.[3]
In this work, we reported ultraviolet photodetectors based on CH3NH3PbCl3 films. The MAPbCl3 layers about 100 nm were prepared via two methods, i.e. a sequential deposition method and dual-source thermal evaporation. For the sequential deposition method, the PbCl2 film was firstly deposited by thermal evaporation on SiO2 (100 nm)/Si (001) substrate, and then the MACl precursor was spin-coated on the top of PbCl2 film. The as-deposited films were finally annealing at 80 oC for 3 hours. The MAPbCl3 films can also be prepared by thermal evaporation using the MACl and PbCl2 sources. The MAPbCl3 perovskite films prepared by both methods show pure cubic MAPbCl3 phase without PbCl2 phase as evidenced by X-ray diffraction. The scanning electron microscope images show the ordered MAPbCl3 grains with size of around 1 µm. The as-deposited films exhibit the photoluminescence peak at 404 nm and the absorption edge at 399 nm, blue-shifted as compared to the MAPbCl3 single crystal due to low trap densities. The UV photodetectors based on MAPbCl3 film were fabricated with the coplanar metal–semiconductor–metal Au finger electrode configuration. The ranges of the finger width and the separated spacing are from 5 to 50 µm for different detectors. The best photodetector exhibited a maximum photoresponse of 5.1mA/W at 360nm at 10 V. The ultraviolet–visible response rejection ratio (the ratio of 360nm to 500nm) was about three orders of magnitude.
[1] Q. Chen, N. De Marco, Y. Yang, T.-B. Song, C.-C. Chen, H. Zhao, Z. Hong, H. Zhou, Y. Yang, Nano Today, 10 (2015) 355-396.
[2] R. Dong, Y. Fang, J. Chae, J. Dai, Z. Xiao, Q. Dong, Y. Yuan, A. Centrone, X.C. Zeng, J. Huang, Adv Mater, 27 (2015) 1912-1918.
[3] G. Maculan, A.D. Sheikh, A.L. Abdelhady, M.I. Saidaminov, M.A. Haque, B. Murali, E. Alarousu, O.F. Mohammed, T. Wu, O.M. Bakr, The Journal of Physical Chemistry Letters, 6 (2015) 3781-3786.
9:00 PM - EP3.3.21
Interface Modification of Hierarchical TiO2 Nanostructures in Lead Halide Perovskite Solar Cells
Oscar Jaramillo-Quintero 1,Pier Bedotto 1,Julio Calva-Yanez 1,Ivan Mora-Sero 2,Marina Rincon 1
1 Instituto de Energías Renovables-Universidad Nacional Autónoma de México Temixco Mexico,2 Institute of Advanced Materials (INAM), Universitat Jaume I Castelló Spain
Show AbstractPerovskite solar cells constitute probably the hottest topic on photovoltaics. Many different structures have been reported for this kind of cells, where a perovskite absorbing layer is basically contacted by electron and hole selecting contacts. These contacts play a dramatic role in the final cell performance.1 Here, we report surface treatment on hierarchical TiO2 nanostructures (HNs), used as electron selecting contact, to reduce the recombination at FTO/TiO2/CH3NH3PbI3 interface. The TiO2 HNs were fabricated by hydrothermal synthesis and treated by different methods to obtain the interface modification. The structural and morphogical characterization were made by XRD and SEM respectively. The perovskite solar cells based on TiO2 were evaluated by Kelvin Probe Force Microscopy (KPFM). The KPFM method measures the distribution of local contact potential difference and electric field across the TiO2/ CH3NH3PbI3 interface of the solar cells. From these measured work functions, we derived the efficacy of surface treatments in modifying interface band alignments, decreasing recombination and improving the efficiency of the overall device.
1. Juarez-Perez, E. J.; Wuβler, M.; Fabregat-Santiago, F.; Lakus-Wollny, K.; Mankel, E.; Mayer, T.; Jaegermann, W.; Mora-Sero, I. Role of the Selective Contacts in the Performance of Lead Halide Perovskite Solar Cells. J. Chem. Phys. Lett. 2014, 5 (4), 680-685.
9:00 PM - EP3.3.22
Transparent Cathode Based Organic-Inorganic Hybrid Perovskite Solar Cell
Md Abdul Kuddus Sheikh 1,Rahim Abdur 1,Daekyun Jeong 1,Bhabani Sankar Swain 1,Jaegab Lee 1
1 School of Advanced Materials Engineering Kookmin University Seoul Korea (the Republic of),
Show AbstractPerovskite solar cells (PSCs) based on organometal halide light absorbers have attracted much attention due to their superb power conversion efficiency (PCE). Perovskite materials have the advantages of low cost, high absorption coefficient, excellent carrier transport, tunable composition and structure as well as the ability to be fabricated by various processing methods. A high photovoltaic performance is attributed to optically high absorption characteristics and balanced charge transport properties as well as long diffusion lengths. Two different cell structures, based on mesoscopic metal oxides and planar heterojunctions have already demonstrated very impressive advances in performance.
Transparent cathode based planar heterojunction organic-inorganic hybrid perovskite solar cell is fabricated with device geometry of ITO/CdS/ CH3NH3PbI3/Spiro OMeTAD/MoO3/Au/MoO3 (MAM). Perovskite film of CH3NH3PbI3 is fabricated via two-step sequential solution deposition using PbI2 in N, N-dimethylformamide (DMF) on to CdS coated ITO glass followed by spin coating of methyl ammonium iodide (MAI). Perovskite film is optimized by varying the experimental variables such as post annealing time, post annealing temperature, methyl ammonium iodide composition with complete conversion of lead iodide to perovskite film. MAM as a transparent triple layer cathode is sequentially deposited by Electronic beam deposition process and optimized by varying the thickness of each layer.
Top and bottom both electrodes are conducting and transparent which leads to illuminate the light from both side of the device.
9:00 PM - EP3.3.23
Encapsulated Perovskite Based Photovoltaics Devices with High Stability
Man Kwong Wong 1,Qi Dong 1,Fangzhou Liu 1,Aleksandra Djurisic 1,Wai Kin Chan 1,Hangkong Li 1,Kaimin Shih 1,Annie Ng 2,Charles Surya 2
1 The University of Hong Kong Pokfulam Hong Kong,2 The Hong Kong Polytechnic University Hung Hom Hong Kong
Show AbstractThe rapidly increasing of power conversion efficiency (PCE) of perovskite based photovoltaics shows a promise to new generation low cost photovoltaic cells. However, it is well recognized that the exposure to moisture, heat and light causes the degradation of perovskite [1] (especially for methylammonium lead iodide (CH3NH3PbI3) which is the most commonly used perovskite material). Guangda Niu and coworkers found that CH3NH3PbI3 decomposed into CH3NH3I solution and PbI2 in the presence of H2O by using UV-Vis spectra and X-ray diffraction (XRD) analysis. [2] Jun Hong Noh and coworkers stated that the PCE of CH3NH3PbI3 based photovoltaics devices decreased by a half after being exposed to high relative humidity level (>55%) for one day only. [3] It makes stability a main issue to perovskite based photovoltaics. It was also found that the perovskite layer decomposed when the devices were aging at high temperature and relative humidity level even when the devices were encapsulated. [4] Hence, an advanced encapsulation method is one of the keys to improve the stability. Here we present a comparison study between different encapsulation methods. Perovskite based photovoltaics devices were encapsulated using different epoxies, with or without the addition of desiccant and the deposition of SiO2 layer. By minimizing the ingress of moisture and oxygen, devices with storage in ambient air under one sun illumination at high relative humidity level (>65%) could retain >90% of the initial performance (PCE around 16%) after one week.
[1] T.-B. Song, Q. Chen, H. Zhou, C. Jiang, H.-H. Wang, Y. M. Yang, Y. Liu, J. You and Y. Yang, J. Mater. Chem. A, 2015, 3, 9032-9050.
[2] G. Niu, W. Li, F. Meng, L. Wang, H. Dong and Y. Qiu, J. Mater. Chem. A 2014, 2,705.
[3] J. H. Noh, S. H. Im, J. H. Heo, T. N. Mandal, and S. I. Seok, Nano Lett. 2013, 13, 1764−1769.
[4] H. Zhou, Q. Chen, G. Li, S. Luo, T.-B. Song, H.-S. Duan, Z. Hong, J. You, Y. Liu and Y. Yang, SCIENCE, 2014, 345, 542-546.
9:00 PM - EP3.3.24
Highly Flexible Perovskite Solar Cells on High-Performance Transparent Crystalline ITO/Metal NW Composite Electrode Film
Hyeon-Gyun Im 1,Seonju Jeong 1,Jungho Jin 2,Jung-Yong Lee 1,Byeong-Soo Bae 1
1 KAIST Daejeon Korea (the Republic of),2 University of Ulsan Ulsan Korea (the Republic of)
Show AbstractInorganic/organic metal halide perovskite solar cells are under an intense spotlight due to their high power conversion efficiencies (PCEs), low-cost and earth-abundance making them a promising power generation source. Recently, flexible perovskite solar cells are intensively studied because they are attractive for various applications such as power-generating clothing, flexible display devices and portable electronic chargers. To date, flexible perovskite solar cells are mostly fabricated based on transparent conducting oxides (TCO) bottom electrodes such as tin-doped indium oxide (ITO). Kelly et al., for example, reported a flexible perovskite solar cell with PCE of 10.2 % on ITO/PET substrate, and Jung et al. reported the cell PCE of 12.2 % on ITO/PEN substrate.[1, 2] However, it is not a simple task to prepare TCO-based flexible perovskite cells that enable reliable performance against repeated bending due to the inherent brittleness of TCO. Herein, we report highly flexible perovskite solar cells on high-performance crystalline ITO/metal NW composite electrode (c-ITO/metal NW-GFRHybrimer) film. It is challenging to fabricate the perovskite solar cells directly on metal NW TCE due to the high reactivity of the metal NW towards halides. The excellent chemical stability of the c-ITO/metal NW-GFRHybrimer films against perovskite precursor solution enables stable integration of perovskite layer. The device structure is c-ITO/metal NW-GFRHybrimer/PEDOT:PSS/perovskite/PCBM/BCP/Ag, and methyl ammonium lead iodide (CH3NH3PbI3) was used as perovskite active layer. The devices on the c-ITO/AgNW- and c-ITO/CuNW-GFRHybrimer films exhibit PCE of 10.16 % and 9.33 %, respectively. We also investigate the bending durability of the devices according to the different bending radii (r = 5 and 2.5 mm). The devices exhibit superior bending stability up to 500 bending cycles.
[1] D. Liu, T. L. Kelly, Nature Photon. 2013, 8, 133.
[2] B. J. Kim, D. H. Kim, Y.-Y. Lee, H.-W. Shin, G. S. Han, J. S. Hong, K. Mahmood, T. K. Ahn, Y.-C. Joo, K. S. Hong, N.-G. Park, S. Lee, H. S. Jung, Energy Environ. Sci. 2015, 8, 916.
9:00 PM - EP3.3.25
Vacuum-Free Perovskite Solar Cells with Fully Slot-Die Coated Layers
Jueng-Eun Kim 2,Yen-Sook Jung 2,Youn-Jung Heo 2,Kyeongil Hwang 2,Sehyun Lee 1,Yeong-A Kim 1,Seung-Hoon Lee 1,Yunseul Kim 1,Doojin Vak 2,Dong-Yu Kim 1
1 GIST Gwangju Korea (the Republic of),2 Flexible Electronics Laboratory CSIRO Clayton Australia,1 GIST Gwangju Korea (the Republic of)2 Flexible Electronics Laboratory CSIRO Clayton Australia
Show AbstractPower conversion efficiency of the state-of-the-art perovskite solar cells is approaching that of commercialized silicon solar cells. Although this solution processed photovoltaic technology has a great potential to be manufactured with a low-production cost, rapid research progress of solution processed perovskite solar cells has been made by a non-scalable spin coating process. Herein, we report single-step slot die coating process for the fabrication of CH3NH3PbI3 based planar perovskite layer. Slot die coating is a scalable coating method and has been widely used for large scale production of organic solar cells which has almost identical fabrication process as planar perovskite solar cells. It is found slot-die coating tends to produce over grown perovskite crystal with a very poor surface coverage. Therefore, we previously adopted more reliable sequential process to produce high performance printed perovskite solar cells with a gas assisted slot die coating. However, it is more ideal to produce devices by less steps. Therefore, we developed the single step deposition process. We found deposition temperature plays critical role. Slot die coating was carried out on heated substrate with gas blowing and effect of deposition temperature on device performance was studied. In addition, we developed conducting inks that can be deposited directly on perovskite layers. Therefore, vacuum-free fully printed perovskite solar cells with a simple device configuration are demonstrated.
9:00 PM - EP3.3.26
Enhanced Photoluminescence in Formamidinium Lead Trihalide Thin Films
Hong-Hua Fang 1,Feng Wang 2,Sampson Adjokatse 1,Ni Zhao 2,Maria Loi 1
1 Univ of Groningen Groningen Netherlands,2 Chinese University of Hong Kong Hongkong Hong Kong
Show AbstractFormamidinium lead iodide (FAPbI3) has a broader absorption spectrum and current voltage characteristics more stable than the one of the most common methylammonium lead iodide, thus FAPbI3 exhibits great potential in photovoltaic application. In this report, the light-induced photoluminescence (PL) evolution in FAPbI3 thin films is investigated. We find that the photoluminescence evolution is strongly dependent on the atmosphere surrounding the samples. When the film is exposed to air, its photoluminescence intensity is enhanced as high as 140 times after continuous two-hours laser illumination, and the average lifetime is prolonged from 17 ns to 389 ns. The enhanced photoluminescence implies that the materials quality is improved in the films that have been illuminated in air. Evidences that this effect originates from moisture-assisted laser-healing will be reported. This result represents an important step to improving the film quality and contributes to the development of perovskite solar cells.
9:00 PM - EP3.3.27
Air Stable (CH3NH3)3Bi2I9 as Light Harvester for Solid State Sensitized Solar Cells
Mutalifu Abulikemu 1,Samy Ould-Chik 2,Xiaohe Miao 3,Erkki Alarousu 1,Guy Olivier Ngongang Ndjawa 1,Jeremy Barbe 1,Abdulrahman ElLabban 1,Silvano Del Gobbo 1
1 SPERC, Physical Sciences and Engineering KAUST Thuwal Saudi Arabia,2 KCC, Physical Sciences and Engineering KAUST Thuwal Saudi Arabia3 KAUST Core Laboratories KAUST Thuwal Saudi Arabia
Show AbstractAs an alternative to the well-assessed lead halide perovskite (CH3NH3PbI3) employed in solid state sensitized solar cells, we investigated the compound (CH3NH3)3Bi2I9 which according to some dated reports possesses interesting optoelectronic properties potentially suitable for photovoltaic applications1-3. The material was synthesized as a powder by reacting Bi2O3 and CH3NH3I in concentrated HI at 120 °C. Alternatively, it was prepared by dissolving BiI3 and CH3NH3I in polar solvents. Thin films of the material were casted onto glass and ITO and TiO2 substrates for optoelectronic investigation and fabrication of photovoltaic devices. In parallel, macroscopic single crystals were grown by the antisolvent diffusion method 4 which allowed for the first time to determine the crystal structure of (CH3NH3)3Bi2I9 by single crystal X-Ray diffraction. It was found that the material crystallizes in hexagonal space group P63/mmc with a crystal structure characterized by two face-sharing BiI6 octahedra forming isolated dimeric [Bi2I9]3- anions separated by two CH3NH3+ cations. Of fundamental importance is that, the material showed in every form a very high stability toward humidity and oxygen. Surface photovoltage spectroscopy (SPS) measurements evidenced outstanding photocharge generation properties in the visible range (<700 nm) comparable to lead halide perovskites. Transient absorption measurements on thin film and single crystal highlighted a long lifetime hole-electron couple in a wide wavelength range. UV-photoelectron spectroscopies and photoelectron spectroscopy in air along with optical diffuse reflectance measurements allowed determining electronic levels. Similarly to a previous report 2,3, it was found a band gap of 1.96 eV for single crystal and 2.6 eV for thin films with excitonic peak onset at 2.26 eV. Finally, a set of photovoltaic devices having the FTO/TiO2/(CH3NH3)3Bi2I9/spiro-MeOTAD/Au architecture were fabricated. Promising but still low values of efficiency were obtained probably due to the short diffusion length of the carriers in the material.
References:
1 Jakubas, R., Zaleski, J. & Sobczyk, L. Phase-Transitions in (CH3NH3)3Bi2I9 (MAIB). Ferroelectrics 108, 109-114, doi:Doi 10.1080/00150199008018741 (1990).
2 Kawai, T. et al. Optical absorption in band-edge region of (CH3NH3)3Bi2I9 single crystals. J Phys Soc Jpn 65, 1464-1468, doi:Doi 10.1143/Jpsj.65.1464 (1996).
3 Kawai, T. & Shimanuki, S. Optical Studies of (CH3NH3)3Bi2I9 Single-Crystals. Phys Status Solidi B 177, K43-K45, doi:DOI 10.1002/pssb.2221770128 (1993).
4 Shi, D. et al. Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals. Science 347, 519-522, doi:10.1126/science.aaa2725 (2015).
9:00 PM - EP3.3.28
Tunable Tin-Based Organo-Halide Perovskite Light Emitting Diodes at Near-Infrared Emission
May Ling Lai 1,Timothy Y. S. Tay 1,Aditya Sadhanala 1,Sian Dutton 1,Guangru Li 1,Richard Friend 1,Zhi Kuang Tan 1
1 University of Cambridge Cambridge United Kingdom,
Show AbstractThe achievement of high efficiency photovoltaics using hybrid organo-lead perovskite (1) attracted significant attention and research, leading to advancement in the optoelectronics sector. Recently, we demonstrated the first working light-emitting diodes using lead halide perovskites (2) paving way to high-efficiency solution processable display devices. The advantages of having easy solution-processing technique, low-temperature heating, excellent semiconducting properties and high performance however are impeded by the concern of toxicity of lead. Here, we have successfully resolve the toxicity issue by replacing lead with a tin variant in our light-emitting devices. The lead-free devices gave the same level of performances as their lead-based counterparts, despite the ion replacement. The tin halide perovskite material is alloyed with different bromide and iodide contents, and is tunable at red and near-infrared electroluminescence. By increasing the bromide content, the semiconductor bandgap increases giving shorter wavelength emissions and is tunable from 945 nm down to 667 nm. We achieved a 945 nm near-infrared emission with a maximum external quantum efficiency of 0.72% and radiance of 3.4 W sr-1 m-2. The deep spectral emission into the infrared widens their scope of applications towards optical communication and signalling systems. These findings in the environmentally-benign hybrid perovskite light-emitting diodes will no doubt provide insights to further explore the suitability of this material in optoelectronic applications.
(1) Lee, M. M., Teuscher, J., Miyasaka, T., Murakami, T. N. & Snaith, H. J. Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites. Science 338, 643-647 (2012).
(2) Tan, Z.-K. et al. Bright light-emitting diodes based on organometal halide perovskite. Nat Nano 9, 687-692 (2014)
9:00 PM - EP3.3.29
Understanding the Structure-Performance Relationship of Perovskite Solar Cells by a Comprehensive Fluorescence Approach
Zhihua Xu 1
1 Department of Chemical Engineering Univ of Minnesota-Duluth Duluth United States,
Show AbstractWe utilize comprehensive fluorescence techniques to investigate the fundamental structure-performance relationship of perovskite solar cells. By a synergetic combination of steady-state and time resolved photoluminescence, ensemble and spatial-revolved PL lifetime and PL spectra, and excitation intensity and electrical field dependent PL, we are able to reveal how the device configurations affect the perovskite film structures and device performance including the power conversion efficiency and hysteresis level.
9:00 PM - EP3.3.30
Time-of-Flight Electron and Hole Drift Mobility Measurements and Dispersive Transport in Perovskite Solar Cells
Brian Maynard 1,Qi Long 1,Eric Schiff 1,Mengjin Yang 2,Kai Zhu 2,Ranjith Kottokkaran 3,Hisham Abbas 3,Vikram Dalal 3
1 Syracuse University Syracuse United States,2 NREL Golden United States3 Iowa State University Ames United States
Show AbstractWe report electron and hole drift mobility measurements on perovskite solar cells from our laboratories. The mobility measurements are based on the standard photocarrier time-of-flight technique using a 5 ns flash of 660 nm light through the front interface. Electrons and holes were distinguished by using positive and negative bias voltages across the cells. To the best of our knowledge, these are the first time-of-flight measurements in cells, and the first electron (minority-carrier) mobilities to be reported.
For a VOC = 0.8 V methyl ammonium lead iodide cell from Iowa State University, we measured an electron mobility μd,e = 1.4 cm2/Vs at room-temperature for a standard ratio d/E = 2x10-8 cm2/V of the sample thickness d and the electric field E. We specify d/E because the electron mobility was “dispersive”, meaning that the mobility has a power-law dependence on d/E: μd,e ∝ (d/E)1-1/α. Here a is the “dispersion parameter”; α=1 corresponds to non-dispersive transport. The electron dispersion parameter was 0.54; with this dispersion, the drift mobility will rise nearly as the reciprocal of d/E, with much larger mobilities for shorter length (and time) scales. The hole mobility and dispersion parameter for this cell were 0.22 cm2/Vs and 0.71, respectively. For a VOC=0.9 V cell made at NREL, we have obtained fairly similar mobilities with greater dispersion.
These modest values for the mobilities have significant implications for the device physics of the cells. In particular, carrier collection under sunlight is likely to be on the boundary between space-charge limitation and ambipolar diffusion-length limitation; a similar situation applies in champion efficiency thin-film nanocrystalline silicon cells, which have similar mobilities to those reported here. In addition, low mobilities are often associated with recombination processes that are diffusion-limited. With diffusion-limited recombination, a low mobility increases the open-circuit voltage, assuming the recombination center density is unchanged.
The presence of dispersion certainly complicates device modeling, but it also offers insight into the fundamental transport mechanism for electrons and holes. The two best-known mechanisms for dispersive transport are (i) an exponential distribution of trap binding energies and (ii) transport on a fractal-like spatial structure. These mechanisms can be distinguished by temperature-dependent measurements. We have also performed these measurements, and we can rule out the trapping model.
This research has been supported by the National Science Foundation (CBET-1336134 & 1336147).
9:00 PM - EP3.3.31
Beyond Efficiency: The Challenge of Stability in Mesoscopic Perovskite Solar Cells
Yaoguang Rong 1,Xiong Li 1,Hongwei Han 1,Zhuan Zhu 1
1 Huazhong University of Science and Technology Wuhan China,
Show AbstractOver the past five years, the rapid emergence of a new class of solar cell based on mixed organic–inorganic halide perovskite semiconductors has captured the attention of scientists and researchers in the fi eld of energy conversion. Benefiting from the optimization of perovskite film deposition approaches, the design of new material systems, and the diversity of device concepts, the efficiency of perovskite solar cells (PSCs) has increased from 2.19% in 2006 to a certified 20.1% in 2014, making this the fastest-advancing solar cell technology to date. However, as a photovoltaic technology, which needs to meet the requirements of working under long-term sunlight, PSCs suffer stability concerns for both materials and devices. Evolved from dyesensitized solar cells (DSSCs), PSCs usually contain a mesoporous electron transporting layer or scaffold layer, a perovskite active layer, a hole transporting layer and a back contact to construct a mesoscopic-structured device. Using interface engineering, mesoscopic PSCs (MPSCs) have obtained exciting stability with a hole-conductor-free printable triple-layer architecture or conventional heterojunction version. Herein, the achievements of mesoscopic solar cells from solid-state DSSCs to MPSCs are outlined and summary of recent progress in the stability of MPSCs is presented. Possible degradation mechanism and solutions are presented and, finally, challenges for the commercialization of this photovoltaic technology are discussed.
9:00 PM - EP3.3.32
Characterization and Critical Control of Intermediate Phase Transformation for Efficient Perovskite Photovoltaic Devices
Yaoguang Rong 2,Swaminathan Venkatesan 2,Xin Zhong 3,Zhongjia Tang 3,Arnold Guloy 3,Yan Yao 2,Zhuan Zhu 4
1 Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology Wuhan China,2 Department of Electrical and Computer Engineering University of Houston Houston United States,2 Department of Electrical and Computer Engineering University of Houston Houston United States3 Department of Chemistry University of Houston Houston United States4 University of Houston Houston United States
Show AbstractMorphology and phase composition are two critical factors that need to be controlled for attaining high efficiency in planar-heterojunction perovskite solar cells based on methyl ammonium lead halide (MAPbX3, X = Cl, Br, I). We firstly investigated an effective solvent engineering process to enable controlled perovskite crystal growth for depositing uniform and compact perovskite thin films. Mixed solvents of DMF/DMSO and DMSO/GBL were employed to prepared the precursor solution. During the spin-coating process, an orthogonal solvent of toluene was dripped to quench the wet films, forming a homogeneous and compact intermediate phase film. After thermal annealing, the intermediate phase transformed to perovskite phase, leading to the formation of a compact perovskite thin film. The crystal structure of the organic-based lead iodide intermediate phase was identified, which was critical in controlling the crystal growth and optimizing thin film morphology. With different delay time for dripping toluene, the particle size and morphology of the perovskite thin films were optimized. Then, we studied the phase transformation in such solvent quenched perovskite thin films and correlated it with device performance. We investigated the role of intermediate phase crystal of MA2PbX3(DMSO)2 and fine-tuned the phase transformation to attain compact and ultra-smooth perovskite films. Two key aspects have been identified namely that the phase transformation kinetics involve both methyl ammonium halide (MAX) and DMSO exchange and morphology is dependent on the phase composition of film. By functioning as a morphology stabilizer during the annealing process, which can prevent undesired decomposition or evaporation, the intermediate phase film was able to convert to an ultra-smooth and compact perovskite film (roughness ~12 nm). Devices fabricated with these films as active layers possessed high fill factor (FF) and open-circuit voltage (Voc). Complete removal of intermediate phase results in the formation of PbI2 which in turn leads to rougher morphology and lower FF and Voc. With an optimal annealing process, a power conversion efficiency over 15% was achieved. Also, the influence of the phase transformation on film morphology and device performance has been discussed, which will benefit the understanding of functional intermediates, formation kinetics, and morphology control of organic-inorganic hybrid halide perovskites.
9:00 PM - EP3.3.33
Effect of Low Thermal Budget Annealing on Solution Processed Organolead Halide Perovskite Semiconductors
Santanu Bag 2,John Berrigan 1,Michael Durstock 1
1 Air Force Research Laboratory Wpafb United States,2 National Research Council Washington United States,1 Air Force Research Laboratory Wpafb United States
Show AbstractMethylammonium lead trihalide perovskites are technologically intriguing compound semiconductor materials, and have received significant attention in the quest for creating new types of electronic and optoelectronic devices that are limited with existing materials. In particular, the development of flexible photovoltaic devices based on roll-to-roll (R2R) compatible deposition techniques are believed to be highly benefited from using this semiconductor materials as solar cell absorbers. However, the successful integration of this material system to low-cost R2R manufacturing technology requires robust processes that overcome the temperature limitation imposed by polymer substrates. Conventional annealing techniques to grow high quality perovskite films are time consuming and often limited due to the thermal instability of the materials above 130°C. In attempt to reduce the thermal budget during perovskite thin-film growth, two unconventional annealing techniques, namely photonic curing and cold zone annealing have been applied to grow CH3NH3PbI3 films in a planar p-i-n type solar cell device structure, and their effects on film morphology and device performance are investigated. As the thin-film absorber layer morphology primarily determines the fundamental properties of the photovoltaic devices, such an understanding and control of the film growth is of critical importance for achieving better device performance.
9:00 PM - EP3.3.34
3D ToF-SIMS Imaging of Perovskite/Titania/FTO in Humid Environments
Wei-Chun Lin 1,Hsun-Yun Chang 2,Jing-Jong Shyue 2,Clemens Burda 3
1 Macromolecular Science and Engineering Case Western Reserve University Cleveland United States,2 RCAS Academia Sinica Taipei Taiwan1 Macromolecular Science and Engineering Case Western Reserve University Cleveland United States,3 Department of Chemistry CWRU Cleveland United States
Show AbstractAbstract: Understanding the stepwise degradation is a crucial thrust for improving the stability and durability of perovskite solar cells since they were discovered as a material for the next generation photovoltaic devices. In this work we demonstrate that CH3NH3PbI3 perovskite degradation, at a high constant humidity, is related to a slow vaporization process of CH3NH2. The degradation process of CH3NH3PbI3 perovskite sample is examined directly by using a time-of-flight secondary ion mass spectrometry (ToF-SIMS) using pulsed Bi3++ as the primary ion and in situ high-energy Ar2500+ gas cluster ion beam (GCIB) as sputtering source. 3D images were reconstructed from this sputter-and-view scheme to illustrate the distribution of the penetrating moisture in the specimen. It is observed that the initial attack occurs via proton exchange on the organic molecule. The intermediate products of this degradation reaction are analyzed and will be presented. This degradation-vaporization process leads to a noticeable change in morphology and color of the perovskite crystal.
9:00 PM - EP3.3.35
Observation of CH3NH3PbI3 Diffusion into the Titania Layer during Operation of Perovskite Solar Cells
Wei-Chun Lin 1,Lili Wang 2,Wei-Lun Kao 3,Yun-Wen You 3,Xin Guo 4,Jing-Jong Shyue 5,Clemens Burda 4,Hsun-Yun Chang 5
1 Macromolecular Science and Engineering Case Western Reserve University Cleveland United States,2 Department of Chemistry Case Western Reserve University Cleveland United States3 Materials Science and Engineering National Taiwan University Taipei Taiwan4 Materials Science and Engineering Case Western Reserve University Cleveland United States3 Materials Science and Engineering National Taiwan University Taipei Taiwan,5 RCAS Academica Sinica Taipei Taiwan1 Macromolecular Science and Engineering Case Western Reserve University Cleveland United States,2 Department of Chemistry Case Western Reserve University Cleveland United States,4 Materials Science and Engineering Case Western Reserve University Cleveland United States5 RCAS Academica Sinica Taipei Taiwan
Show AbstractThis study demonstrates the degradation process of perovskite solar cells under different device operation times. The degradation process of perovskite solar cells was examined directly by X-ray photoelectron spectroscopy (XPS) and in situ low-energy Ar+ sputtering for depth profiling. We show that this analytical technique clearly indicates the elemental depth profile of perovskite solar cells (Ag/Spiro-OMeTAD/Perovskite/meso-TiO2/Compact TiO2/FTO). Devices operated for different testing times are subjected to this profiling technique for studying the change of elemental distribution. It was found that perovskite has longer diffuse depth towards the TiO2 layer after actual use. It was also observed that iodine diffused into the Ag anode after the devices were operated multiple times. It has been shown before that perovskite solar cells have higher power conversion efficiency after the devices were operated a few times. The diffusion of perovskite material into the TiO2 layer can explain this unexpected improvement observed by several research groups in the perovskite field.
9:00 PM - EP3.3.36
Modulated Polarization and Electrical Measurements to Reveal the Nature of Hysteresis in Hybrid Perovskite Solar Cells
Md Nadim Ferdous Hoque 1,Mengjin Yang 2,Nazifah Islam 1,Kai Zhu 2,Zhaoyang Fan 1
1 Department of Electrical and Computer Engineering Texas Tech University Lubbock United States,2 Chemistry and Nanoscience Center National Renewable Energy Laboratory Golden United States
Show AbstractThe fundamental mechanism governing the anomalous I-V hysteresis phenomenon in the hybrid perovskite solar cells (PSCs) has been in debate. Understanding the mechanism will help develop better materials and structures to obtain stable and practical PSCs. Here, we report our electrical studies, through the modulation of electrical field, temperature, light illumination, and structural phase transition, to reveal the dominance of ion migration effect on the hysteresis phenomena.
In this study, we measured the polarization hysteresis and remnant polarization charge density in PSCs under different modulations using the Positive-Up-Negative-Down (PUND) method. The polarization study, under the control of field, temperature and optical excitation, reveals that ferroelectric property of the perovskite material cannot be the decisive factor for the anomalous I-V hysteresis phenomenon at typical operating temperatures. Ion migration, with a relatively small activation energy for tetragonal phase CH3NH3PbI3, should be dominant mechanism. This conclusion was further supported by impedance and DC electrical characterization and structural phase transition characterization.
With this understanding, we further report the comparative studies on mesoporous and planar PSCs with different hysteresis behavior, to provide guidance on the proper device design toward hysteresis-free PSCs.
9:00 PM - EP3.3.37
Acid Free Method for Conductivity Enhancement in PEDOT: PSS Thin Films as Flexible Transparent Electrodes in Perovskite Solar Cells
Bjorn Vaagensmith 1,Eman Gaml 1,Khan Reza 1,Nick Kantack 1,Ashish Dubey 1,Qiquan Qiao 1
1 South Dakota State University Brookings United States,
Show AbstractPerovskite solar cells have attracted much attention due to their solution processability and recent significant improvement in power conversion efficiency. Transparent conducting oxide such as indium tin oxide (ITO) or Florien tin oxide (FTO) are typically used as the transparent electrode for perovskite solar cells. However, ITO and FTO are rigid, high cost and vacuum deposited; moreover, devices which are entirely solution processed or vacuum deposition processed are preferable, unlike ITO and FTO solar cells. Therefore, there is a strong need to develop a transparent solution processed electrode fully compatible with roll to roll processes on flexible substrates. In this study we present an acid free method for enhancing the conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) by using solvent additive blends and solvent blend post treatments. We found the solvent blend additive of DMSO:EG (1:1) with a post treatment in water:ethanol:ethanlene glycol (1:1:1) bath to provide the best conductivity enhancement. We propose the additive provides a duel mechanism for conductivity enhancement by inducing a quinoid PEDOT structure and disrupting static interaction between the PEDOT and PSS polymers, where the post treatment helps remove excess PSS from the film. The best mixed halide perovskite solar cell device showed a power conversion efficiency of 5.7% with PEDOT:PSS as the transparent electrode, as compared to a power conversion efficiency of 8.7% of the best ITO based device.
9:00 PM - EP3.3.39
Electric Field Induced Slow Transient Optoelectronic Response in MAPbI3 Probed With Dynamic Photoluminescence
Daniel Jacobs 1,Michael Scarpulla 2,Benjamin Bunes 1,Chen Wang 1,Ling Zang 1
1 Materials Science and Engineering University of Utah Salt Lake City United States,1 Materials Science and Engineering University of Utah Salt Lake City United States,2 Electrical and Computer Engineering University of Utah Salt Lake City United States
Show AbstractOrganic-inorganic hybrid perovskite photovoltaics have shown impressive performance growth to over 20% in the past decade. However, further material and device optimization is becoming increasingly limited by the unique slow transient response from the active layer, namely methylammonium lead triiodide (MAPbI3). Several mechanisms have been proposed to explain this slow electrical transient including a ferroelectric effect, charge trapping, and ion migration. However, the sensitivity of the MAPbI3 film to the fabrication technique, interface effects, and environmental conditions makes determining an intrinsic response mechanism very challenging. In this work, we introduce a multifunctional testing platform capable of monitoring the slow transient optoelectronic response of MAPbI3 to an applied electric field by way of dynamic photoluminescence (PL) spectroscopy, microscopy, and current measurements on a lateral interdigitated electrode structure. By systematically varying the applied bias magnitude and polarization directions, we observed distinct fast reversible and slow irreversible PL transient responses in the form of spectrally and spatially resolved PL quenching occurring over a range of 0.3 to 100 seconds. By directly correlating the simultaneous optical and electrical transient responses, the slower irreversible response was attributed to ionic migration under electronic fields far lower than what is present in working perovskite solar cell devices. These findings showcase the potential of this testing platform to analyze the complex optical and electrical response in MAPbI3 with temporal, spectral and spatial resolution to gain a deeper and more detailed understanding of this exciting material.
9:00 PM - EP3.3.40
Characterization and Analysis of Structural Properties, Crystallography and Surface Potential of Perovskite Thin Films
Shaimum Shahriar 1,Cheik Sana 1,Vanessa Castaneda 1,Robert Cotta 2,Deidra Hodges 1,Edison Castro 3,Luis Echegoyen 3,Tahmina Akter 3,Geoffrey Saupe 3,Eva Deemer 2,Russell Chianelli 3
1 Electrical and Computer Engineering The University of Texas at El Paso El Paso United States,2 Metallurgical, Materials and Biomedical Engineering The University of Texas at El Paso El Paso United States3 Department of Chemistry The University of Texas at El Paso EL PASO United States
Show AbstractThe development of perovskite thin films by spin-coating, deposition techniques have been investigated. The methyl ammonium lead iodide (CH3NH3PbI3) perovskite has a direct band gap of 1.5 eV and a large absorption coefficient of over 2×104 cm-1. It was deposited by a non-vacuum liquid-based coating method with 2 steps using Laurell Technologies WS650 spin processor. Characterization and analysis of structural properties, crystallography, surface roughness and surface potential of perovskite were performed by using the Thermo Scientific DXR Smart Raman spectrometer, the Perkin Elmer spectrum 100 Fourier Transform Infrared spectrometer (IR spectrometer), Hitachi S-4800 Scanning Electron Microscope (SEM), the Bruker D8 Discover X-ray diffractometer (XRD), the NT-MDT Ntegra Atomic force microscopy (AFM), KLA-Tencor D-120 Profilometer and the Scanning Kelvin Probe Microscopy (SKPM). Results were used to determine the fingerprint of each element, the crystal structure, orientation and crystallite size, surface roughness and surface potential of perovskite thin films. Raman peaks of perovskite appear at 62 cm-1, 94 cm-1, 110 cm-1, 119 cm-1, 154 cm-1 and 250 cm-1 wave number. IR spectroscopy identifies the methyl –CH3, N-H, C-H, C-N and M-X (metal – halide) bonds. at 2870 cm-1, 3400 – 3500 cm-1, 1020 – 1220 cm-1 and at 750 cm-1 wave number. The XRD diffraction peaks, (110), (202), (220), (312), (224) and (314) were found at 14.077°, 24.47°, 28.354°, 31.768°, 40.48° and 43.09°. The uniformity and compact crystalline nature were observed in the films by SEM. The roughness, thickness, crystalline and dense-grained uniform morphology with grain sizes were exhibited by AFM. The mean of area, volume, z distance, perimeter, diameter, length, width, aspect ratio of grains were 0.053 µm×µm, 26.468 µm×µm×nm, 348.9 nm, 0.412 µm, 0.078 µm, 0.137 µm, 0.039 µm, 0.036 µm/µm. The surface roughness of perovskite thin film was 79.2 nm and the thickness of the layer was ~ 330 nm which were determined by profilometer. The film surface potential around 200 mV. The surface potential difference change is resulted from newly formed PbI2 phases. It affects the device performance by changing the carrier behavior at the relevant interfaces.
9:00 PM - EP3.3.42
Differences of Perovskite Film Morphologies in Various Precursor Systems
Sehyun Lee 1,Seung-Hoon Lee 1,Jueng-Eun Kim 1,Yeong-A Kim 1,Jin-Mun Yun 2,Dong-Yu Kim 1
1 School of Materials Science and Engineering GIST Gwangju Korea (the Republic of),2 Radiation Research Division for Industry and Environment Korea Atomic Energy Research Institute (KAERI) Jeongeup-si Korea (the Republic of)
Show AbstractPerovskite solar cells (PeSCs) have attracted great attention according to one of the best candidates as next power sources due to their excellent optoelectronic properties such as direct bandgap, excellent charge transport, high absorption coefficient, and defect tolerability. Although PeSCs with high power conversion efficiency (PCE) up to 20 % were recently reported by S.-I. Seok et al, the understanding of forming perovskite crystalline structure mechanism were seldom reported to be associated with device performance variations. To figure out the relationship between perovskite crystal morphology and device performances, we introduced only small amount of solvent as additives into the N,N-dimethylformamide (DMF) based precursor solution. Several solvents, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N-cyclohexyl-2-pyrrolidone (CHP), N-octyl-2-pyrrolidone (NOP), Benzyl benzoate (BB), and Benzyl ether (BE), were selected as additives followed by their some properties such as vapor pressures, boiling points, and the amide functional group. Among these additives, the precursor with CHP showed best PCE and the smallest device-to-device deviation due to the proper vapor pressure (~ 0.05 mmHg at 25 °C) and the existence of amide group. Finally, perovskite film morphologies of various precursor systems and device performances were evaluated by Grazing Incidence X-ray Diffraction, Scanning Electron Microscope, etc.
9:00 PM - EP3.3.43
Lead free (CH3NH3)3Bi2I9 Perovskite for Optoelectronic Applications
Trilok Singh 1,Tsutomu Miyasaka 1,Ashish Kulkarni 1
1 Graduate School of Engineering, Toin University of Yokohama Toin University of Yokohama Yokohama Japan,
Show AbstractThe organic-inorganic trihaloplumbate perovskite semiconductors (CH3NH3PbX3, X = Br, I, Cl) with 3-D perovskite structure have gained tremendous interest as light harvesting materials in thin-film photovoltaics due to their outstanding light-absorption characteristics, charge-transport dynamics and simple processability using solution or vapour-phase deposition techniques, or a combination thereof. Recently, research efforts worldwide have led to an incredible increase in power conversion efficiencies beyond 20% using lead based perovskite. However, the lead-based perovskite solar cells suffer from the low chemical stability in air and moisture, and more importantly the toxicity of lead is an obstacle for further commercialization. Lead-free devices such as tin analogues (CH3NH3SnI3) have been shown to exhibit moderate performances. However, these devices suffer serious problems in particular stability against moisture
The present talk will address the possibility to replace lead by a non-toxic heavy p-block metal, organic-inorganic methylammonium iodo bismuthate perovskite based photovoltaic and its suitability for the futuristic solar cells. Furthermore, physicochemical and optoelectronic properties of the planar/meso heterojunction solid-state device of reported perovskite will be discussed in details.
9:00 PM - EP3.3.44
Stable Semi-Transparent CH3NH3PbI3 Planar Sandwich Solar Cells
Jin Hyuck Heo 1,Sang Hyuk Im 1
1 Kyung Hee University Yongin-si Korea (the Republic of),
Show AbstractThe solar energy has attracted a great deal of attention as promising candidate replacing conventional fossil fuels because it is renewable, clean, sustainable, and abundant enough to satisfy energy demand for human beings on the earth. The solar energy can be easily converted electric energy which is the most convenient energy form by solar cells. Most population of people is concentrated in a city and consequently the consumption of electric energy is mainly consumed in the city. Therefore, it is quite reasonable to directly generate the convenient electricity in the city such as building window. For this application, the semi-transparent solar cells should be developed because the window should transmit the visible light. From this point of view, thin film solar cells are useful to be applicable to building integrated photovoltaics (BIPVs). Here, we fabricated semi-transparent perovskite sandwich solar cells by using two TCO electrodes like the solid-state dye-sensitized solar cells by lamination method. The perovskite sandwich solar cells exhibited 15.8 % of average power conversion efficiency and great air and humidity stability over 20 days due to self-passivated architecture of sandwich solar cells.
9:00 PM - EP3.3.45
Modulating Electron - Hole Interaction in a Hybrid Lead Halide Perovskite with Electric Field
Tomas Leijtens 2,Srinivasa Maruthi Ajay Ram Srimath Kandada 1,Giles Eperon 2,Giulia Grancini 1,Valerio D'Innocenzo 3,James Ball 1,Samuel Stranks 4,Henry Snaith 2,Annamaria Petrozza 1
1 Istituto Italiano di Tecnologia, CNST Milano Italy,2 University of Oxford Oxford United Kingdom,1 Istituto Italiano di Tecnologia, CNST Milano Italy2 University of Oxford Oxford United Kingdom1 Istituto Italiano di Tecnologia, CNST Milano Italy,3 Politecnico di Milano Milano Italy4 MIT Cambridge United States
Show AbstractDespite rapid developments in both photovoltaic and light emitting device performance, the understanding of the optoelectronic properties of hybrid lead halide perovskites is still incomplete. In particular, the polarizability of the material[1,2], the presence of molecular dipoles, and their influence on the dynamics of the photo-excitations[3] has remained an open issue to be clarified. Here, we investigate the effect of an applied electric field, both at room temperature and at low temperature, on the photo-excited species by monitoring the photoluminescence (PL) yield and PL decays[4].
At room temperature (RT), we find that an applied electric field quenches the photoluminescence, as expected from field induced carrier separation and drift. However, we also find a significant reduction in the non-radiative monomolecular decay rate. The latter occurs on a slow (minutes) timescale, suggesting that mobile defects, which can drift under application of an electric field, are, at least in part, responsible for the non-radiative decay pathway.
We also performed the same experiment at 190K, in order to reduce the influence of temperature activated processes. We find that the radiative decay rate is greatly enhanced and we even observe evidence for rapid geminate recombination after the application of the electric field. The result is an increase in relative PLQY by up to 10 % after applying a field of 150 KV cm-1. Combining these findings with electric field dependent Raman spectroscopy, we propose that the electric field induces an alignment and “locking” of the organic dipoles. This reduces their ability to screen the excited state Coulomb interactions and disrupts the electric fields within the polarized domains. The result is a strengthened electron – hole interaction. This work sheds new light on the crucial effect of the molecular dipole on electron – hole interactions in hybrid lead halide perovskites.
References
[1] Xiao, Z. et al. Giant switchable photovoltaic effect in organometal trihalide perovskite devices. Nat Mater .14, 193–198(2015).
[2] Snaith, H. J. et al. Anomalous Hysteresis in Perovskite Solar Cells. J. Phys. Chem. Lett. 5, 1511-1515 (2014).
[3] Grancini, Kandada et al. Role of microstructure in the electron-hole interactions of hybrid lead-halide perovskites, Nat. Photonics, 9, 695-701 (2015).
[4] Leijtans, Kandada et al. Modulating Electron - Hole Interaction in a Hybrid Lead Halide Perovskite with Electric Field, manuscript under revision.
9:00 PM - EP3.3.46
High Performance and Stable Perovskite Solar Cells with Modified Electron Transport Layer
Seongmin Kang 1,Heetae Yoon 1,Jong-Kwon Lee 1,Mansoo Choi 1,Nam-Gyu Park 2
1 Seoul National Univ Seoul Korea (the Republic of),2 Sungkyunkwan Univ. Suwon Korea (the Republic of)
Show AbstractRequirement for renewable energy is becoming increased with a wide interesting in new types of solar cell industry due to their positive potential for clean energy resource replacing fossil fuel. Recently, solid-state perovskite solar cell using methylammonium lead iodide (CH3NH3PbI3) as a light harvester has attracted much attention with excellent photovoltaic properties. Since the first report on the 9.7% power conversion efficiency (PCE) of the perovskite solar cells, there have been intensive attempts to improve the performances of the devices. As a result, PCE of 20.1% was recorded as the highest certificated value in 2014. However, one of critical challenges of organometallic halide perovskite materials is unstable hysteresis of J-V curves with respect to the scan direction. Therefore, reducing hysteresis of perovskite solar cells with high efficiency is important for long term stability. We demonstrate an electron transport layer (ETL) modified perovskite solar cells with stabilized PCE over 18%. Mesoporous TiO2 ETL, which has the necessity of a 500 °C sintering step, is replaced using compact thin film of organic based ETL by low temperature evaporation process. We optimized the ETL with a various experimental results in terms of thickness, deposition rate and materials for high performance and stable perovskite solar cells. Such reproducible and stabilized perovskite solar cells were turned out to have best efficiency of 18.2% irrespective of the scan rate. It enables perovskite solar cells to have feasibility potential for further improvement in stabilized high efficiency and practical application.
9:00 PM - EP3.3.48
The Effect of the Film Microstructure on the Light Soaking Effect in Hybrid Perovskite Solar Cells
Shuyan Shao 1,Mustapha Abdu-Aguye 1,Jian Liu 1,Gert ten Brink 1,Lamber Jan Anton Koster 1,Maria Antonietta Loi 1
1 Zernike Institute for Advanced Materials University of Groningen Groningen Netherlands,
Show AbstractOver the past five years, intensive research efforts have been devoted to improving the power conversion efficiency (PCE) of the hybrid perovskite solar cells, which produce PCE higher than 20%. However, little attention has been paid to understand their operating mechanism. As a result, several unusual properties of perovskite solar cells, such as hysteresis, switchable photovoltaic effect and light soaking effect, have not been completely understood. In this study we investigated how the microstructures of the perovskite film influence the photo-response of the solar cells under continuous light illumination. Photoluminescence (PL) measurements indicate that perovskite film with uncompact morphology in the film shows much slower photo-response compared to perovskite film with compact morphology. This result demonstrates the slow response of the perovskite film with voids is due to the much higher density of surface traps which takes longer time for the photo-generated free carriers to fill in. In agreement with the PL results, the device adopting uncompact perovskite film shows slow and larger improvement in device performance under continuous light illumination, while the device adopting compact perovskite film shows almost constant device performance. The improved device performance is mainly due to the enhanced VOC and FF. The device adopting uncompact perovskite film shows a VOC of 0.83 V, a FF of 0.66 and a PCE of 10.6% after one and a half hours of light soaking compared to a VOC of 0.42 V, a FF of 0.47 and a PCE of 3.8% before light soaking. The device adopting perovskite film with compact morphology shows a VOC of 0.83 V, a FF of 0.68 and a PCE of 10.3% after light soaking compared to a VOC of 0.8 V, a FF of 0.65 and a PCE of 9.5% before light soaking. These results indicate controlling the microstructure of the perovskite film is an effect way to eliminate the slow light photo-response in perovskite solar cells.
9:00 PM - EP3.3.49
Controlled Crystallization of Hybrid Perovskite Thin Films for Efficient Planar Perovskite Solar Cells
Sampson Adjokatse 1,Shuyan Shao 1,Mehrdad Najafi 1,Hong-Hua Fang 1,Thomas Palstra 1,Maria Loi 1
1 Zernike Institute for Advanced Materials University of Groningen Groningen Netherlands,
Show AbstractOrganic-inorganic halide perovskite materials have become pre-eminent in photovoltaic technology because of the high light-harvesting capabilities demonstrated in perovskites such as methylammonium lead halides, MAPbX3 (X = Cl, Br, I). Although the first perovskite-sensitized solar cell was reported only in mid-2009, having power conversion efficiency of 3.8%, the past five years have seen an unprecedented rapid progress with energy conversion efficiencies exceeding 20%. Nonetheless, several pressing open questions remain, among which include the control of crystallization and morphology, the source and elimination of hysteresis, the influence of interlayers, charge transfer dynamics etc.
In this work, the deposition of the compact perovskite thin film is accomplished using the one-step method. However, unlike the conventional one-step method where the spin-coated perovskite film is directly followed by annealing at an elevated temperature, the as-deposited film is kept at room temperature under vacuum to regulate the crystal growth and perovskite formation. This new method proves to be a better technique for controlling perovskite crystallization and film uniformity than the conventional method that typically contains significant number of defects. Devices based on this technique gave maximum power conversion efficiency (PCE) above 14 %. Thus, this new perovskite thin film processing route allows for better control of crystallization and reduction of defects, making it a more robust processing technique.
9:00 PM - EP3.3.50
The Temperature Dependency on the Photovoltaic Performance of Planar- Heterojunction Perovskite Solar Cells
Eunseon Jeong 1,Jae-Wook Kang 1
1 Jeonbuk National Univ. Jeon-ju Korea (the Republic of),
Show AbstractOrganometal halide perovskite have attracted considerable attention over the past several years due to their great potential for photovoltaic applications and recently considered as promising materials in lasing and light emitting device. Although the first efficient solid-state perovskite cells were reported only in mid-2012, extremely rapid progress was made during 2015 with energy conversion efficiencies reaching a confirmed 20% at the end of the year. In this report, a brief discussion is presented regarding the operating temperature on the photovoltaic parameter of PSCs. The device architecture consist of planar structure of solution processed of PbI2 and methylamoniumiodide (MAI), where the solution-processed zinc oxide (ZnO) and 2,2',7,7'-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene was used as electron and hole transporting layer, respectively. The current-voltage measurement was recorded by adjusting the temperature using thermoelectric device from -25 to 25 oC. The maximum Voc, Jsc and PCE of solar cells seem to be more appropriate at 253K. Also photoluminescence and XRD of perovskite have different phenomena at low temperature. Furthermore, the stability under 1 sun light illumination was tested as a function of operating temperature.
9:00 PM - EP3.3.51
The Nucleation and Growth Evolution of the Perovskite Films by Dual-Source Thermal Evaporation
Haitao Xu 1,Yanglin Wu 1,Wenzhen Wang 1,Run Xu 1,Fei Xu 2,Linjun Wang 1
1 School of Materials Science and Engineering Shanghai University Shanghai China,2 Department of Physics, Instrumental Analysis amp; Research Center Shanghai University Shanghai China
Show AbstractOrganometal halide perovskite recently becomes the most competitive candidate for absorber materials of solar cells due to the remarkable photovoltaic performances. Besides the widely adopted solution-based method, vacuum deposition is also a general way to prepare the perovskite films due to its high surface coverage, low roughness and precise control of the film thickness. However, compared with the widely explored perovskite growth mechanism of solution-based method, the underlying growth mechanism of perovskite films by vacuum techniques has not been studied in detail. In addition, the initial growth and the evolution of perovskite films may help us to understand the origin of high series resistance and low fill factor that are often observed in the evaporation-based perovskite solar cell.
In this work, the nucleation and evolution of the perovskite films on the ITO, pedot/ITO, FTO, TiO2/FTO, Si and glass substrates are studied. Both the scanning electron microscope images and atomic force images show that a Stranski–Krastanow-like evolution mode was observed for the growth of the perovskite films. The 2D-like regions are firstly formed at the very initial stage, and become to a continuous surface featured with large smooth regions at the equivalent film thickness of 10-20nm. After this stage, some small 3D ordered island grains begin to nucleate at the intersection region between large smooth regions or the defects on the surface of large smooth regions. These ordered grains become larger with increasing the film thickness, and finally cover completely the 2D regions at the film thickness around 150-250nm for different substrates.
We also found that X-ray diffraction is a useful method to study the initial growth of MAPbI3 since both MAPbI3 and PbI2 are strongly preferred orientation growth on a flat substrate such as Si and glass, making the distinguish of PbI2 and MAPbI3 at the initial stage of films with thickness of 5nm possible. At the very initial growth stage, the films consist of mainly PbI2 and a small part of MAPbI3. Moreover, this PbI2 mediated growth is likely the key reason that leads to the 2D growth. These PbI2 can be reduced and even eliminated completely with the evolution of film growth due to the vertical diffusion of MAI molecular.
The Stranski–Krastanow-like evolution mode seems a universal mode for the perovskite on all substrates adopted in our experiment. These results give a clear indication that the complex interface mixed with PbI2 and MAPbI3 may limit electron transportation from the perovskite layer to the conductive layer and increase the recombination center, which may result in the high series resistance and low fill factor that often happens in the evaporation-based perovskite solar cells.
9:00 PM - EP3.3.52
Flexibility of Perovskite as Investigated by Micro-Tensile Testing
Seung-Min Ahn 1,Eui Dae Jung 1,Myoung Hoon Song 1,Ju-Young Kim 1
1 UNIST Ulsan Korea (the Republic of),
Show AbstractExploring alternative energy sources is a highly important assignment in the world. The sun is a sustainable, reliable and almost infinite source of energy that can make significant contributions to the global demand for energy. Organic-inorganic halide perovskite solar cells have been studied as attractive candidates for highly efficient solar cells. The photovoltaic efficiency of perovskite-based solar cells has recently soared rapidly from 3.8% to above 20%. Methylammonium lead halide (CH3NH3PbX3, MAPbX3) perovskites holds promise for highly effective next-generation photovoltaic devices. Such perovskite-based devices have many advantages: remarkable optical properties, longer electron-hole diffusion lengths, high light absorption coefficients and good cost-effectiveness, and show promise not only in photovoltaic applications but also in other applications such as luminescent devices and transistors. However, these materials are still afflicted with long-term stability problems due to organic-inorganic bonding between decomposed perovskite and disturbed hydrogen because of the high polarity of water molecules. Recently, perovskite devices have attracted substantial attention for flexible/stretchable electronic devices, so that their mechanical properties are important for device reliability and durability. Some researchers have recently explored the elastic properties of perovskite-based solar cells using nanoindentation tests. Unfortunately, these nanoindentation tests can evaluate such properties only quantitatively, since such properties are strongly affected by substrates or under layers. In addition, it is difficult to determine the mechanical properties of stretchable in the pulling direction. For this reason, here we fabricate various free-standing perovskite layers and evaluated tensile mechanical properties using small-scale tensile tests. Perovskite active layers of various thicknesses were fabricated using solution processes such as spin-coating and drop casting and then were separated in different ways depending on thickness. The tensile mechanical properties related to flexible/stretchable behavior were analyzed by a nano-tensile tester in laboratory with 1 nm working resolution. This study of mechanical properties of MAPbX3 perovskites should be useful in research on solar cell durability and fundamental mechanisms.
9:00 PM - EP3.3.53
Color Tunable Electroluminescent Diodes Based on Hybrid 3D Perovskite Semiconductors
Naresh K. Kumawat 1,Amrita Dey 1,Aravindh Kumar 2,K. L. Narasimahan 2,Dinesh Kabra 1
1 Department of Physics Indian Institute of Technology Bombay Powai, Mumbai India,2 Electrical Engineering Indian Institute of Technology Bombay Powai, Mumbai India
Show AbstractHybrid 3D perovskite (ABX3; A = CH3NH3+, B = Pb2+ and X= I-, Br- or Cl-) semiconductor is the new wave in solar cells research area with cell efficiencies more than 20% within a time span of few years.[1, 2, 3, 4] This is just a big surprise for semiconductor community that a solution processible material, which can crystallize even at room temperature can show very high quality optoelectronic properties as an important ingredients for Lasers [5] and LEDs [6] too.
We study structural, morphological and optical properties of ABX3 by replacing halide anion (X-) to tune the electronic band gap (Eg). We systematically tune the bandgap towards visible range to exploit these materials for light-emitting applications. We demonstrate electroluminescence at NIR (ABI3-xClx), Red (ABI1.25Br1.75), Green (ABBr3) [7] and first report about ABBr1.08Cl1.92 based blue light emitting diode at room temperature. We note that unlike ABI3, the wider band gap perovskites have significantly high exciton binding energy and cannot be ignored to determine the true value of electronic Eg. We established Vegard’s law for this and fit our UV-Vis data with generalized Elliot’s theory of Wannier exciton model. [8]
Reference:
[1] H.-S. Kim et al Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9% Scientific Rep. 2012, 591, 1-7.
[2] M. M. Lee et al Efficient hybrid solar cells based on meso-superstructured organometal halide perovskites Science 2012, 338, 643-647.
[3] N. J. Jeon et al Solvent engineering for high-performance inorganic–organic hybrid perovskite solar cells Nat. Mater. 2014, 13, 897–903.
[4] H. Zhou et al Interface engineering of highly efficient perovskite solar cells Science 2014, 345, 542-546.
[5] G. Xing et al Low-temperature solution-processed wavelength-tunable perovskites for lasing Nat. Mater. 2014, 13, 476-480.
[6] Z.-K. Tan et al Bright light-emitting diodes based on organometal halide perovskite Nat. Nanotech. 2014, 9, 687-692.
[7] N. K. Kumawat et al Near Infrared to Visible Electroluminescent Diodes Based on
Organometallic Halide Perovskites: Structural and Optical Investigation ACS Photonics 2015, 2, 349-354.
[8] N. K. Kumawat et al Band Gap Tuning of CH3NH3Pb(Br1−xClx)3 Hybrid Perovskite for Blue Electroluminescence ACS Appl. Mater. & Interfaces 2015, 7, 13119−13124.
Symposium Organizers
Kai Zhu, National Renewable Energy Laboratory
Jinsong Huang, University of Nebraska–Lincoln
Maria Antonietta Loi, University of Groningen
Tsutomu Miyasaka, Toin University of Yokohama
Symposium Support
Aldrich Materials Science
Applied Physics Letters | AIP Publishing
EP3.4: Device and Processing III
Session Chairs
Jinsong Huang
Ivan Mora-Sero
Wednesday AM, March 30, 2016
PCC North, 200 Level, Room 224 B
9:00 AM - *EP3.4.01
The Challenge of Printing and Processing Perovskite
Trystan Watson 1,Jenny Baker 1,Eifion Jewell 1,Joel Troughton 1,Peter Greenwood 1,Katherine Hooper 1,Daniel Burkitt 1,Simone Meroni 1,Daniel Williams 1,Francesca De Rossi 1
1 SPECIFIC, Swansea University Swansea United Kingdom,
Show AbstractWhilst photovoltaic efficiency of Perovskite solar cells continues to increase, attention is also being paid to the manufacturing processes that are required to scale these lab devices into modules for high volume sheet to sheet or roll to roll fabrication on low cost substrates such as glass and metal foils.
This paper will introduce a series of technology developments required to enable the continuous fabrication of perovskite solar cells at commercial scale. This will include a layer by layer approach to coating deposition including the mechanisms and process parameters required to successfully deposit perovskite and hole transport materials via slot die and blade coating.
Slot die coating of the perovskite active layer can replace laboratory spin coating as a continuous deposition process. This method pumps the perovskite precursor through a die perpendicularly onto the moving substrate below, allowing for variables such as flow rate, coating speed and die substrate gap to be tuned to give a thinly deposited wet film on either metal or glass substrates. Unlike spin coating there is no dynamic solvent removal and therefore during the annealing step significant solvent evaporation takes place during perovskite nucleation. If not tightly controlled this can cause heterogenous nucleation of the perovskite which can increase the roughness of the final film. Solvent evaporation also carries and redistributes the solids in the precursor yielding thicker and thinner sections depending on the evaporation front as it moves across the substrate.
Additional challenges for metal mounted perovskite solar cells entail reengineering the evaporated electrode to produce a transparent alternative. Our approach to overcoming this with a polymer film embedded nickel grid and transparent conducting adhesive will be presented.
The paper will conclude by presenting the wide range of coating and curing options available for the large scale fabrication of perovskites followed by a critical assessment as to the most appropriate.
9:30 AM - *EP3.4.02
An Integrated Approach Combining Compositional and Interfacial Material Engineering to Improve the Performance and Stability of Perovskite Solar Cells
Alex Jen 1
1 Univ of Washington Seattle United States,
Show AbstractThe potential for perovskite photovoltaics to create transformative energy generation is currently restrained by its reliability issues regard hysteresis and degradation. In order to address these challenges, we have employed an integrated material, interface, and device engineering approach to establish perovskite structure-property relationships and interfacial material design rules to enable rational design of highly efficient and stable devices. This has resulted in devices with both high power conversion efficiency (PCE of >18%) and minimum hysteresis. The mechanistic insight we build directly toward hysteresis can be extended to address issues related to degradation and stability. This integrated design approach will have the potential to address these issues at their source, enabling better and timely design of suitable perovskite compositions and interfacial materials to facilitate technology translation to industry.
10:00 AM - EP3.4.03
Metal Oxide Management for Low-Cost and Durable Lead Halide Perovskite Solar Cells
Tsutomu Miyasaka 1
1 Toin University of Yokohama Yokohama Japan,
Show AbstractPhotovoltaic performance and stability of organo-lead triiodide perovskite absorbers can be optimised by selecting the carrier collection materials in junction with perovskite. While TiO2 has been widely used as electron collector for methylammonium (MA) perovskite, Al2O3 serves as a better hydrophilic scaffold for perovskite crystal formation and improves hole blocking ability against recombination. We could obtain high conversion efficiency (>17%) of MAPbI3 prepared on meso-Al2O3 layer by increasing open circuit voltage (Voc) and reducing hysteresis [Miyasaka, Chem. Lett. 2015, 44, 720]. Voc is often enhanced by improving the crystallinity and surface structure of TiO2 layer. This improvement can also lead to make cells with minimal hysteresis and high durability under ambient air. Recently, we found that brookite TiO2 (bk-TiO2) works an excellent electron collector in terms of stronger inter-particle necking and more uniform film than anatase TiO2. bk-TiO2 film is prepared by low-cost sinter-free (low temperature) process. Among other low-cost metal oxide semiconductors, SnO2 and ZnO also suit low temperature preparation (<150 oC). Both of SnO2 and ZnO, when used as electron collectors of MAPbI3, exhibited efficiency of 13-14% maintaining high Voc >1.0V. In application to optoelectronics, a thin metal oxide layer plays a key role in regulating photodiode performance of the perovskite. We could devise high-sensitivity photodetecting diode based on simple junction of MAPbI3 and TiO2 compact layer, in which reverse bias-driven amplified current density was strongly enhanced by the bypass-rich structure of TiO2. Interestingly, defect-less dense compact layers are unable to contribute to current amplification. Optimised photodetector achieved light-detecting sensitivity up to 620 Ampere per incident power (W) against weak mono-chromatic light (mW/cm2), under small bias voltage (0.3-0.9V).
10:15 AM - EP3.4.04
Energy Disorder Correlated Open-Circuit Voltage in Hybrid Perovskite Solar Cells
Yuchuan Shao 1,Yongbo Yuan 1,Jinsong Huang 1
1 Department of Mechanical and Materials Engineering Univ of Nebraska-Lincoln Lincoln United States,
Show AbstractOrganometal trihalide perovskites have been demonstrated as excellent light absorbers for high efficiency photovoltaic applications. One origin of the high PCE of the perovskite solar cells is their relatively large ratio of the open-circuit voltage (VOC) to bandgap (Eg) of ~ 0.691. However, their VOC/ Eg ratio is still lower than that of the amorphous silicon and GaAs thin film solar cells of 0.801. Giving the first-order charge-recombination rate in OTP materials have been shown to be so weak due to the unusual defect physics2, there is still a large potential to further increase PCE of OTP solar cells by boosting VOC.
In the past, great efforts have been focused on the optimizing the grain morphology of the perovskite thin films to increase the perovskite solar cell efficiency. Here, we demonstrate that the energy disorder of electron transport layer has a significant impact on the VOC of the perovskite solar cell devices, which opens a new paradigm for perovskite solar cell design3.
We show that a simple solvent annealing method can effectively reducing the energy disorder of the electron transport layer which is phenyl-C61-butyric acid methyl ester (PCBM) in our case. After solvent annealing treatment, the VOC of the CH3NH3PbI3 planar heterojunction solar cells is increased from 1.04 V to 1.13 V without comprising the short circuit current and fill factor, which boosts the steady-state PCE from 17.1 % to 19.4 %. The photocurrents showed negligible hysteresis, as a result of the effective deactivation of surface and grain boundary charge traps by the double fullerene layers in our devices4. The energy disorder parameter, density of states (DOS) and photogenerated charge carrier concentration rate in the perovskite solar cells with different PCBM treatments are directly measured. The measured energy disorder is also supported by a recent independent theoretical work5 which reported the same disorder parameter for ordered and disordered PCBM.
1 Green, M. A., Emery, K., Hishikawa, Y., Warta, W. & Dunlop, E. D. Solar cell efficiency tables (Version 45). Progress in photovoltaics: research and applications 23, 1-9 (2015).
2 Yin, W.-J., Shi, T. & Yan, Y. Unusual defect physics in CH3NH3PbI3 perovskite solar cell absorber. Applied Physics Letters 104, 063903 (2014).
3 Shao, Y., Yuan, Y. & Huang, J. Energy Disorder Correlated Open-Circuit Voltage in Hybrid Perovskite Solar Cells. Nature Energy, In revision (2015).
4 Shao, Y., Xiao, Z., Bi, C., Yuan, Y. & Huang, J. Origin and elimination of photocurrent hysteresis by fullerene passivation in CH3NH3PbI3 planar heterojunction solar cells. Nature communications 5 (2014).
5 Tummala, N. R., Zheng, Z., Aziz, S. G., Coropceanu, V. & Brédas, J.-L. Static and Dynamic Energetic Disorders in the C60, PC61BM, C70, and PC71BM Fullerenes. The Journal of Physical Chemistry Letters 6, 3657-3662, (2015).
10:30 AM - EP3.4.05
Role of Charge Extracting Layers in the Stabilization of the J-V Characteristics of Inverted Hybrid Perovskite Solar Cells
Mario Caironi 1,Michele De Bastiani 2,Giorgio Dell'Erba 3,Marina Gandini 3,Valerio D'Innocenzo 3,Stefanie Neutzner 1,Mirko Prato 1,Annamaria Petrozza 1
1 Istituto Italiano di Tecnologia Milano Italy,1 Istituto Italiano di Tecnologia Milano Italy,2 Università degli Studi di Padova Padova Italy1 Istituto Italiano di Tecnologia Milano Italy,3 Politecnico di Milano Milano Italy
Show AbstractSolution-processable hybrid perovskite semiconductors have risen to the forefront of photovoltaics research, offering the potential to combine low-cost fabrication with high power-conversion efficiency. The observation of slow transient and hysteretic effects observed in perovskite-absorber devices, which severely affects current density–voltage (J-V) measurements and efficiency determination, has further stimulated deeper exploration of the working mechanisms of opto-electronic devices. Several groups have recently and independently demonstrated that, by applying an electric field across a pristine film of 3D hybrid perovskites of different chemical composition, a self-sustained field is induced in the semiconductor as a consequence of ion migration towards the electrode regions. A variety of dynamics have been reported, which differ in magnitude and time scale, depending both on the specific device architecture and, in particular, on the adopted charge extraction layer, highlighting a considerable effect of contact interfaces on transients in perovskite based devices.
Here we report on the role played by charge extracting layers on the slow transient behavior of CH3NH3PbI3 perovskite based solar cells [1]. Such transients are found to notably modify the open circuit voltage also in the very first J-V scans of so called “hysteresis-free” devices integrating a Phenyl-C61-butyric acid methyl ester (PCBM) charge extraction layer. Here a pre-conditioning of the device, i.e. a repetition of J-V scans, is needed to achieve completely stable J-V characteristics under illumination. In particular, we find that under device operation, iodide ions migrate to the electron extracting layer. While ions transport is typically associated with charge extraction efficiency, we first show that the use of an organic extraction layer such as PCBM, albeit not hampering ions motion, evidently improves charge extraction with respect to interfaces involving compact TiO2. Moreover, we show that ions can specifically interact with the organic electron extracting layer, inducing electronic doping and that such I-/PCBM interaction is at the origin of the pre-conditioning requirement for stabilizing the device and for improving its open circuit voltage with respect to the first scan.
[1] M. De Bastiani, M.Caironi*, A. Petrozza* et al., Advanced Energy Materials 2015, DOI: aenm201501453(201501453)
10:45 AM - EP3.4.06
High Efficient Planar-Heterojunction Solar Cells Achieved by Using a Smooth CH3NH3PbI3 Film via a New Approach of Forming the PbI2 Nanostructure Together with Strategically High CH3NH3I Concentration
Wallace Choy 1,Hong Zhang 1,Jian Mao 1,Hugh Zhu 1
1 Univ of Hong Kong Hong Kong China,
Show AbstractIn a typical two-step sequential deposition of perovskites such as MAPbI3 (MA=CH3NH3+), PbI2 is first deposited on the substrate (mesoporous or planar scaffold) by spin-coating or vacuum evaporation, subsequently transformed into the perovskite (MAPbI3) by exposing it to an anhydrous isopropanol (IPA) solution of MAI. For the two-step sequential deposition, the conversion and film morphology of the final perovskite film strongly depend on the initial PbI2 film during the first step of the process. Conventionally, PbI2 from dimethyl formamide (DMF) solution tends to form a layered and dense crystalline film on a flat substrate. However, the complete conversion of PbI2 to perovskite on exposure to the MAI solution usually requires several hours. However, this long reaction time in MAI solution could lead to the dissolution of perovskites. These drawbacks make it difficult to fabricate planar-structured PSCs by sequential deposition method. To our knowledge, a simple and effective method for fast conversion of PbI2 film into perovskite on flat substrate via two-step sequential deposition process at room temperature has not been reported. Although many groups have demonstrated the PbI2 residue in perovskite film has a positive effect on the efficiency of PSCs, the effect of PbI2 residue on the long-term stability of PSCs is unclear.
In this work, we demonstrate a new approach for forming the PbI2 nanostructure and the use of high CH3NH3I concentration which are adopted to form high quality (large crystal size and smooth) perovskite film with better photovoltaic performances. On one hand, self-assembled porous PbI2 is formed by incorporating small amount of rationally chosen additives into the PbI2 precursor solutions, which significantly facilitate the conversion of perovskite without any PbI2 residue. On the other hand, through employing a relatively high CH3NH3I concentration, a firmly crystallized and uniform CH3NH3PbI3 film is formed. As a result, a promising power conversion efficiency (PCE) of 16.21% is achieved in planar-heterojunction PSCs. Furthermore, we experimentally demonstrate that the PbI2 residue in perovskite film has a negative effect on the long-term stability of devices.
H. Zhang, J. Mao, H. He, D. Zhang, H.L. Zhu, F. Xie, K.S. Wong, M. Grätzel, W.C. H. Choy, "A smooth CH3NH3PbI3 Film via a New Approach for Forming the PbI2 Nanostructure Together with Strategically High CH3NH3I Concentration for High Efficient Planar-Heterojunction Solar Cells", Adv. Energy Mat., DOI:10.1002/aenm.201501354.
11:30 AM - *EP3.4.07
Highly Efficient Hysteresis-Less Perovskite Solar Cells
Sang Hyuk Im 1
1 Kyung Hee University Yongin-si Korea (the Republic of),
Show AbstractSince Grätzel et al. reported efficient solid-state dye-sensitized solar cells (D-SSCs), intensive studies have been done to develop cost-effective next generation solar cells in order to further reducing the power generation cost of conventional crystalline Si (c-Si) solar cells. The next generation solar cells such as organic photovoltaics (OPVs), inorganic thin-film solar cells, D-SSCs, quantum dots solar cells (QDSCs), and perovskite solar cells have been of great interest for several decades to develop efficient solar cells. Unfortunately, the power generation cost of most next generation solar cells were not satisfactory to compete with that of conventional c-Si solar cells mainly due to the lower overall power conversion efficiency than c-Si solar cells. Recently, liquid junction perovskite sensitized solar cells were reported by Kojima et al. and then intensive studies have been being done until now to develop solid-state perovskite solar cells with high efficiency and low cost. Currently the record efficiency of perovskite hybrid solar cells reached over 20%] and is gradually reaching to the efficiency of c-Si solar cell. However, the perovskite hybrid solar cells are known to have significant current density-voltage (J-V) hysteresis with respect to the scan direction and scan rate. The origin of J-V hysteresis has not been exactly elucidated and it is still debating. The considered possible reasons are dipolar orientation of ferroelectricity, ionic motion of ionic crystalline perovskite material, and trap/detrapping by the unbalanced flux of charge carriers. The ferroelectricity and ionic motion is dealing with the intrinsic properties of hybrid perovskite materials so that to solve the hysteresis problem, significant effort seems to be required to develop newly designed perovskite materials but the later one seems to be relatively simple and easy to control/solve the J-V hysteresis. Here I would like to introduce systematic study of my group to reduce the J-V hysteresis of perovskite solar cells and share recent progress of my group.
12:00 PM - *EP3.4.08
The Interplay of Nanostructure, Perovskite Film and Interface and Its Impact on Photovoltaic Performance
Shihe Yang 1
1 Hong Kong Univ of Samp;T Kowloon Hong Kong,
Show AbstractHybrid organic/inorganic perovskite solar cells continue to attract the interest of a wide community of researchers. One of the outstanding features of the perovskite materials is their solution processibility while forming high-quality films for photovoltaic and optoelectronic devices. In order to improve the perovskite film growth from solutions, it is important to understand the physical and chemical processes involved. In this contribution, we will present out studies on the interplay of nanostructured electrodes, perovskite films and their interfaces. The impact of the interplay on solar cell performance, including power conversion efficiency, stability, etc., will be discussed through a few examples using specially designed nanobowl array electrode of mesoporous TiO2, sol-gel processed NiO and nanostructured carbon.
12:30 PM - EP3.4.09
Experimental Screening of Mixed-Metal Perovskite Compositions for Improved Performance and Thermal Stability
Matthew Klug 3,Anna Osherov 1,Samuel Stranks 2,Patrick Brown 4,Roberto Brenes 5,Xiangnan Dang 6,Vladimir Bulovic 5,Angela Belcher 6
3 Department of Biological Engineering Massachusetts Institute of Technology Cambridge United States,1 Research Laboratory of Electronics Massachusetts Institute of Technology Cambridge United States1 Research Laboratory of Electronics Massachusetts Institute of Technology Cambridge United States,2 Department of Physics University of Cambridge Cambridge United Kingdom1 Research Laboratory of Electronics Massachusetts Institute of Technology Cambridge United States,4 Department of Physics Massachusetts Institute of Technology Cambridge United States4 Department of Physics Massachusetts Institute of Technology Cambridge United States,5 Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge United States6 Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge United States1 Research Laboratory of Electronics Massachusetts Institute of Technology Cambridge United States,5 Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge United States3 Department of Biological Engineering Massachusetts Institute of Technology Cambridge United States,6 Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge United States
Show AbstractAlthough solar cells with impressive power conversion efficiencies have been demonstrated using lead-based metal halide perovskites, there are concerns regarding the inherent toxicity and long-term stability of these materials. This work explores whether both of these issues can be simultaneously addressed by fabricating perovskite solar cells with mixed-metal compositions. To do so, an experimental screening study was performed that systematically replaced between 1.56% and 25% of the Pb content in perovskite films with nine different alternative, less-toxic divalent metal species to form methylammonium mixed-metal triiodide perovskite embodiments, denoted as MA(Pb:B')I3, where B' = {Co, Cu, Fe, Mg, Mn, Ni, Sn, Sr, and Zn}. By experimentally evaluating how replacing small, but not insignificant, amounts of lead with transition or alkaline earth metals influences photovoltaic performance, the tolerance of the MAPbI3 material to extrinsic species was empirically evaluated. Findings indicate that several species improve device performance at modest levels of replacement, whereas others are detrimental. Likewise, several compositions produce device efficiencies greater than the pure MAPbI3 baseline when 12.5% or 25% of the Pb is replaced with certain alternative metal species.
In order to explain the observed trends in photovoltaic performance, each of the mixed-metal compositions was investigated with several materials and electronic characterization techniques, including: x-ray diffraction, electron microscopy, and steady-state and time-resolved photoluminescence spectroscopy. The highest performing mixed-metal composition series was further investigated with x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and energy-dispersive x-ray spectroscopy mapping on a film cross-section with TEM. These findings reveal that introducing a second metal species can influence film morphology, modify the material band gap, shift the band edge locations, and impact photoluminescence. The aggregate data provides enough information for us to propose feasible physical mechanisms that explain trends in performance and are consistent with observations. Furthermore, this work also presents preliminary results that suggest some mixed-metal compositions also demonstrate superior resistance to degradation at elevated temperatures. While further experimentation is required to evaluate whether mixed-metal compositions would improve performance of solar cells utilizing different device architectures or perovskite synthesis techniques, this study presents encouraging evidence that introducing alternative metal species can have beneficial impacts on device performance and stability, while simultaneously mitigating toxicity.
12:45 PM - EP3.4.10
Elimination of the Light Soaking Effect and Efficiency Enhancement in Perovskite Solar Cells by Using a High Dielectric Constant Fullerene Derivative as Electron Extraction Layer
Shuyan Shao 1,Mustapha Abdu-Aguye 1,Jian Liu 1,Li Qiu 2,Sampson Adjokatse 1,Machteld E. Kamminga 1,Gert ten Brink 1,Jan C. Hummelen 2,Maria Antonietta Loi 1
1 Zernike Institute for Advanced Materials, University of Groningen Groningen Netherlands,1 Zernike Institute for Advanced Materials, University of Groningen Groningen Netherlands,2 Stratingh Institute for Chemistry University of Groningen Groningen Netherlands
Show AbstractDespite the fast increase in the power conversion efficiency (PCE) of hybrid perovskite solar cells (PVSCs), the fundamental investigations to reveal the operating mechanism of them are still at their early stage. Many open questions remain to be answered; one of the most relevant regards the light soaking effect, which is commonly observed in PVSCs. In this study, we unveil that the light soaking effect in PVSCs originates from the electron trap assisted (TA) recombination. We speculate that electrons in electron extraction layer (EEL) and holes in perovskite layer recombine with each other assisted by the deep-lying interface trap states. Furthermore, we invested how the electron extraction layer deposited on the hybrid perovskite active layer influences the device performance in a p-i-n planar device structure under continuous light illumination. A high dielectric-constant fullerene derivative with ethylene glycol ether (EG) side chains is used as electron extraction layer (PTEG-1) and PC60BM are used as electron extraction layers. PTEG-1 displays a dielectric constant of 5.7, which is higher than that of PC60BM (3.9). The device using PTEG-1 as EEL shows negligible light soaking effect, which shows a PCE of 15.18% before light soaking and a minor increase in PCE to 15.71% after light soaking. In contrast, the device using PC60BM as EEL shows severe light soaking effect, which shows a low PCE of 3.77% before light soaking and a considerable improvement in PCE to 11.69%. Time-resolved and steady state photoluminescence spectroscopy studies indicate that the high dielectric constant PTEG-1 helps to suppress the trap assisted recombination at perovskite/EEL interface due to reduced critical distance, leading to minor light soaking effect and enhanced performance in PVSCs. These results contribute not only to unraveling the physical working mechanism of PVSCs, but gives also guidelines for their improvement.
EP3.5: Physics—Mechanism, Property and Theory I
Session Chairs
Maria Antonietta Loi
Nitin Padture
Wednesday PM, March 30, 2016
PCC North, 200 Level, Room 224 B
2:30 PM - *EP3.5.01
Lead Halide Complex Chemistry Influencing the Properties of Organic Lead Halide Perovskites
Prashant Kamat 1,Joseph Manser 1,Seogjoon Yoon 1
1 Univ of Notre Dame Notre Dame United States,
Show AbstractThe initial complexation between Pb2+ and halide ions (e.g., I-, Br-) plays a crucial role in determining the final form of perovskites. For example, the plumbate complex formed in the precursor solution evolves into a perovskite structure during annealing process. Nearly 7 times larger complexation constant between Pb2+ and Br- as compared to Pb2+ and Cl- can alter the composition of halide ions in the annealed perovskite film. Such complexation is also influential in exhibiting composition dependent excited state behavior in mixed halide perovskites. Furthermore the mobility of halide ions can also be tracked through reversible changes in the emission behavior. Transient absorption spectroscopy measurements also reveal the existence of a charge transfer state in addition to the charge separated state. Results that show photoinduced segregation in mixed halide perovskite will also be discussed.
3:00 PM - EP3.5.02
Slow Hot Carrier Cooling in Caesium Lead Iodide (CsPbI3) Perovskite
Qing Shen 1,Teresa Ripolles 2,Yuhei Ogomi 2,Koji Nishinaka 2,Taro Toytoda 1,Takuya Izuishi 1,Kenji Yoshino 3,Shuzi Hayase 2
1 Univ of Electro-Communications Chofu Japan,2 Kyushu Institute of Technology Kitakyushu Japan3 Miyazaki University Miyazaki Japan
Show AbstractThe interest in organic-inorganic hybrid solid-state solar cells based on organolead halide perovskite has increased over the past three years following the recently reported power conversion efficiency (PCE) of 20.1%. Organolead halide perovskites in the form of AMX3 (A=organic molecule, e.g., CH3NH3(MA), B=Pb, X=Cl, Br, and I) can be simply crystallized from solution at low temperature (≤100 °C), which enables them to be utilized as light absorbing materials in various solar cells. Recently, inorganic caesium lead halide (CsPbX3) perovskite have been reported in working solar cells [1-3], which suggests a potential for making even more stable inorganic perovskite solar cells than the hybrid organic-inorganic materials currently displaying the highest efficiencies.
For future application such as hot-carrier solar cells, electrically pumped lasers, the understanding of photoexcited carrier dynamics, especially hot carrier cooling dynamics are very important. Recently, hot-carrier cooling dynamics in MAPbI3 was reported [4]. In this study, for the first time, we studied ultrafast photoexcited carrier relaxation dynamics, especially hot carrier cooling, in CsPbI3 using a transient absorption (TA) spectroscopy. A clear bleach peak can be observed at the bandgap energy (1.79 eV) in the TA spectrum. We found that during the hot carrier cooling process within a few picoseconds: (1) a sub-bandgap transient absorption signal arises at about 1.75 eV, which can be explained by bandgap renormalization and hot-carrier distribution; (2) the high-energy tail (1.85 eV-2 eV) of the TA spectrum is broadened, which is attributed to the presence of a quasi-equilibrium carrier distribution at a temperature Tc higher than the lattice temperature of the sample. Then we calculate the carrier temperature Tc versus time and the hot carrier cooling rate from the time-resolved TA spectra. It is very interesting that the hot carrier cooling is as slow as 20 ps for higher excitation densities, which is attributed to a ‘phonon bottleneck’. This slow hot carrier cooling time in CsPbI3 is much longer than the reported cooling time in MAPbI3 (a few ps)[4]. Our findings indicate a potential of CsPbI3 for application to hot carrier solar cells.
[1] S. Hayase et al., Solar Energy Materials & Solar Cells, 2015, in press.
[2] H. Snaith et al., J. Mater. Chem. A, 2015, DOI: 10.1039/C5TA06398A.
[3] G. Hodes et al., J. Phys. Chem. Lett., 2015, 150610174239009.
[4] F. Deschler et al., Nature Comm., 2015, DOI: 10.1038/ncomms9420.
3:15 PM - EP3.5.03
Charge Carrier Dynamics in Hybrid Metal Halide Perovskites
Rebecca Milot 1,Waqaas Rehman 1,Giles Eperon 1,Henry Snaith 1,Michael Johnston 1,Laura Herz 1
1 Department of Physics University of Oxford Oxford United Kingdom,
Show AbstractHybrid metal halide perovskites have recently emerged as promising new materials for many optoelectronic applications including photovoltaics. In addition to their near-optimal light absorption properties, their success is due largely to a combination of high charge carrier mobilities, long diffusion lengths, and long carrier lifetimes.1 Questions still remain, however, about the relationship of these properties to changes in chemical composition and physical properties such as temperature. While essential for helping to elucidate the basic physics of these materials, such studies are also important for predicting device behavior.
The photoconductivity in thin films of CH3NH3PbI3, one of the most popular perovskite materials, was investigated from 8 K to 370 K.2 In this temperature range CH3NH3PbI3 undergoes two structural phase changes at 160 K and 310 K. The monomolecular charge-carrier recombination rate was found to increase with rising temperature, indicating a mechanism dominated by ionized impurity mediated recombination. Conversely, the bimolecular rate constant decreases with rising temperature as charge-carrier mobility declines, and the Auger rate constant is highly dependent on phase. High mobility and diffusion length are maintained at high temperature beyond the tetragonal-to-cubic phase transition at ~310K, demonstrating that there are no fundamental obstacles to the operation of photovoltaic cells based on CH3NH3PbI3 under typical field conditions.
The relationship between structure and photoconductivity was further evaluated for mixed-halide formamidinuim lead bromide-iodide perovskites, HC(NH2)2Pb(BryI1–y)3, which are attractive for color-tunable and tandem solar cells.3 Bimolecular and Auger charge-carrier recombination rate constants strongly correlate with the bromide content, y, suggesting a link with electronic structure. FAPbBr3 and FAPbI3 exhibit high charge-carrier mobilities, while mobilities across the mixed Br/I system are all lower and depend on crystalline phase disorder.
References
(1) Wehrenfennig, C.; Eperon, G. E.; Johnston, M. B.; Snaith, H. J.; Herz, L. M. High Charge Carrier Mobilities and Lifetimes in Organolead Trihalide Perovskites. Adv. Mater. 2014, 26, 1584-1589.
(2) Milot, R. L.; Eperon, G. E.; Snaith, H. J.; Johnston, M. B.; Herz, L. M. Temperature-Dependent Charge-Carrier Dynamics in CH3NH3PbI3 Perovskite Thin Films. Adv. Funct. Mater. 2015, 25, 6218–6227.
(3) Rehman, W.; Milot, R. L.; Eperon, G. E.; Wehrenfennig, C.; Boland, J. L.; Snaith, H. J.; Johnston, M. B.; Herz, L. M. Charge-Carrier Dynamics and Mobilities in Formamidinium Lead Mixed-Halide Perovskites. Adv. Mater. 2015, 10.1002/adma.201502969.
3:30 PM - EP3.5.04
Long-Range Diffusion and Recombination of Free Carriers in Perovskite CH3NH3PbBr3 Single Crystals
Takumi Yamada 1,Yasuhiro Yamada 2,Hidetaka Nishimura 1,Yumi Nakaike 1,Atushi Wakamiya 1,Yasujiro Murata 1,Yoshihiko Kanemitsu 1
1 Kyoto Univ. Uji Japan,2 Chiba Univ. Inage Japan
Show AbstractIn recent years, lead halide perovskites CH3NH3PbX3 (X = Cl, I, Br) have attracted much attention as a new class of solar cell materials. The power conversion efficiencies of perovskite solar cells have been drastically improved and exceed 20 % to date [1]. We showed that photogenerated electrons and holes behave as free carriers (no excitonic effects) [2], and long carrier lifetime and long carrier diffusion length are considered to be the important factors for high power conversion efficiencies of perovskite solar cells. We also have revealed the importance of fast free-carrier diffusion on photoluminescence (PL) dynamics in CH3NH3PbI3 single crystals by using time-resolved PL spectroscopy [3]. For application, lead halide perovskites are considered as top cell in tandem solar cells, where the bottom cell materials are Si and CIGS [4]. Unfortunately, the bandgap of CH3NH3PbI3, which is currently the most widely studied perovskite, is smaller than the ideal bandgap for the top cell. Higher-bandgap perovskites are desired and lead bromide perovskites CH3NH3PbBr3 are one of potential candidates for the top cell, because the bandgap is blueshifted when the iodide ion is replaced by the bromide ion [5]. For the development of future solar cell materials, it is beneficial to understand the details of the photocarrier dynamics related to the photoconversion process by investigating the basic optical properties of the bromide perovskite CH3NH3PbBr3 single crystals.
In this study, the photocarrier dynamics in CH3NH3PbBr3 single crystals were studied by using time-resolved PL spectroscopy. To clarify the effects of the spatial photocarrier distribution, the carriers were generated either at the near-surface region by one-photon excitation, or at the interior region by two-photon excitation. Under one-photon excitation, the PL peak redshifted as the time elapsed. On the other hand, the PL peak exhibited no red-shift with time under two-photon excitation. Furthermore, the one-photon excited PL decays were faster than the two-photon excited PL decays. We concluded that the carrier diffusion process at the near-surface region causes the PL peak shift and the rapid decay of the PL intensity under one-photon excitation. By solving the one-dimensional diffusion equation, we evaluated the values of free carrier mobilities.
[1] W. S. Yang et al., Science, 348, 1234 (2015).
[2] Y. Yamada et al., J. Am. Chem. Soc., 136, 11610 (2014).
[3] Y. Yamada, T. Yamada et al., J. Am. Chem. Soc., 137, 10456 (2015).
[4] P. Löper et al., IEEE J. Photovolt., 4, 1545 (2014).
[5] E. T. Hoke et al., Chem. Sci., 6, 613 (2015).
4:30 PM - EP3.5.06
Rapid Photocarrier Trapping in CH3NH3PbI3-Based Solar Cells as Revealed by Time-Resolved Photoluminescence Spectroscopy
Yasuhiro Yamada 1,Takumi Yamada 2,Naoki Maruyama 2,Atushi Wakamiya 2,Yoshihiko Kanemitsu 2
1 Chiba Univ. Chiba Japan,2 Kyoto Univ. Kyoto Japan
Show AbstractHalide-perovskite-based photovoltaic devices recently attract great attention because of the low fabrication cost, high flexibility, and high efficiency exceeding above 20 %. Our research motivation is to find the key features that provide the high photoconversion efficiency of perovskite solar cells. For this purpose, we have so far studied the fundamental optical properties and their dynamical behaviors of halide perovskite CH3NH3PbI3 (MAPbI3) thin films and single crystals by means of time-resolved photoluminescence (PL) and transient absorption spectroscopy [1-4]. We have revealed that the carrier recombination process is dominated by nonradiative single-carrier trapping under weak excitation and electron-hole radiative recombination under strong excitation [2]. This result suggests that excitons are unstable and photoexcited electrons (holes) behave as free carriers at room temperature, which is consistent with the small exciton binding energy (~7 meV) estimated from the near-band-edge optical absorption spectra [3]. For further understandings of photoconversion mechanism, it is needed to study the photocarrier relaxation processes in diode device structures.
In this study, we conducted the time-resolved PL measurements in MAPbI3 thin films, TiO2/ MAPbI3, MAPbI3/Spiro-OMeTAD, and TiO2/MAPbI3/Spiro-OMeTAD structures. In these samples, we observed the fast PL decay (~ 1 ns) under very weak excitation below 10 nJ/cm2, which can be assigned as carrier trapping process into finite numbers of defects and impurities. On the basis of the excitation-fluence dependent PL decay profiles, we can estimate the carrier trap densities.
We will present the estimated carrier trap density of MAPbI3-based structures. Our experiment provides useful information on the trap density formed at the TiO2/MAPbI3 and MAPbI3/Speiro-OMeTAD compared with the bulk trap density. This finding will contribute the further enhancement of the photoconversion efficiency of the perovskite solar cells.
Part of this work was supported by JST-CREST and JST-PRESTO.
References
[1] Y. Yamada et al., Appl. Phys. Express 7, 032302 (2014).
[2] Y. Yamada et al., J. Am. Chem. Soc. 136, 11610 (2014).
[3] Y. Yamada et al., IEEE J. Photovoltaics 5, 401 (2015).
[4] Y. Yamada, et al., J. Am. Chem. Soc. 137, 10456 (2015).
4:45 PM - EP3.5.07
Electronic Interaction and Chemistry at Organic Inorganic Halide Perovskites Interfaces
Philip Schulz 1,Paul Ndione 1,Mengjin Yang 1,Kai Zhu 1,Joseph Berry 1
1 NREL Golden United States,
Show AbstractHybrid organic/inorganic perovskite-based absorbers define a new class of photovoltaic devices which are quickly taking over the lead in maximum power conversion efficiencies in the field of thin-film solar cells.[1] For the complete device the electronic coupling between the perovskite absorber and adjacent charge extraction and transport layer is a critical parameter to maximize cell functionality. In the past we reported how the open circuit voltage can be affected by the alignment of the frontier molecular orbitals in an organic transport layer with the electronic transport level in the perovskite.[2] Furthermore, we found that the doping characteristic of the underlying oxide substrate can be used to rigidly tailor the Fermi level position in a subsequently deposited perovskite film. For future applications such as an integration of a perovskite subcell into a tandem device, the precise control over the electronic alignment processes is required.
Here we present a study to elucidate these mechanisms by examining a selection of oxide charge carrier extraction layers on top of methylammonium (MAPbI3) and formamidinium (FAPbI3) lead iodide perovskite films in this present study. The choice of transparent conductive oxide layers employed ranges across functional n-type (e.g. TiO2, MoOx), p-type (e.g. NiO) and intrinsic oxides (e.g. Al2O3) using pulsed laser and atomic layer deposition techniques. Using ultraviolet and X-ray photoemission spectroscopy (UPS/XPS) we determine the electronic energy level alignment at the oxide/perovskite interface and at the same time track chemically induced changes. Using this approach we are able to explain band offset changes induced in the perovskite layer by either a chemical interaction with the oxide on top and changes in the electrostatic potential. The results are not only used to give a guideline how to integrate oxide layers into perovskite photovoltaic devices but also explain to what extent the electronic structure of the perovskite is subject to extrinsic pertubations on a universal scale.
[1] [1]K. Emery, Best research cell efficiencies. http://www.nrel.gov/ncpv/images/efficiency_chart.jpg, Ed. NREL: 2014
[2] P. Schulz, E. Edri, S. Kirmayer, G. Hodes, D. Cahen, A. Kahn, Energy Environ. Sci. 2014, 7, 1377
[3] P. Schulz. L. L. Whittaker-Brooks, B. A. MacLeod, D. C. Olson, Y.-L. Loo, A. Kahn, Adv. Mater. Interfaces 2015, doi: 10.1002/admi.201400532
5:00 PM - EP3.5.08
Monitoring Chlorine by X-ray Absorption Spectroscopy of PbCl2-Derived Perovskite Film
Aryeh Gold-Parker 2,Vanessa Pool 2,Michael McGehee 1,Michael Toney 2
1 Stanford University Stanford United States,2 SLAC National Accelerator Laboratory Menlo Park United States,2 SLAC National Accelerator Laboratory Menlo Park United States1 Stanford University Stanford United States
Show AbstractThe inclusion of chlorine has been shown to improve carrier diffusion lengths in methylammonium lead triiodide perovskite films (CH3NH3PbI3-xClx) [1]. Preparation from PbCl2 has also demonstrated improved surface coverage and film uniformity as compared to films derived from PbI2 [2], and it has been suggested that residual chlorine may have an effect on perovskite device electronics [3].
We have previously reported that chlorine leaves the film during annealing through sublimation of MACl [4] and that the final films have a residual amount of chlorine ~x=0.05 [5]. In this study, we have investigated the kinetics of of chlorine evolution from PbCl2-derived perovskite films throughout the annealing process. This was done through the use of in-situ X-ray Fluorescence (XRF) at the chlorine K-edge. A 1:3 mix of PbCl2:MAI in DMF was spin-coated on FTO/c-TiO2 in a nitrogen glovebox; in-situ XRF measurements were then performed while the films were annealed in a helium environment. The films were never exposed to ambient air.
We have also performed in-situ X-ray Diffraction measurements, allowing us to compare the kinetics of chlorine evolution to the kinetics of perovskite crystal formation. Surprisingly, for a range of annealing temperatures, the majority of chlorine is observed to leave the film before the perovskite phase begins to form. By understanding these kinetics, we aim to improve film quality and device performance in perovskite solar cells.
[1] S. Stranks et al. Science (2013), 342
[2] Y. Tidar et al., J. Am. Chem. Soc. (2014), 136
[3] S. Colella et al., J. Phys. Chem. Lett. (2014), 5
[4] E. Unger et al., Chem. Mater. (2014), 26
[5] V. Pool et al., Chem. Mater. (2015), 27
5:15 PM - EP3.5.09
Can Ferroelectric Polarization Explain the High Performance of Perovskite Solar Cells?
Tejas Sherkar 1,Lamber Jan Anton Koster 1
1 Zernike Institute for Advanced Materials University of Groningen Groningen Netherlands,
Show AbstractThe power conversion efficiency of photovoltaic cells based on the use of hybrid halide perovskites, CH3NH3PbX3 (X = Cl, Br, I), now exceeds 20%. Recently, it was suggested that this high performance originates from the presence of ferroelectricity in the perovskite, which is hypothesized to lower charge recombination in the device. Here, we investigate and quantify the influence of mesoscale ferroelectric polarization on the device performance of perovskite solar cells. We implement a 3D drift diffusion model to describe charge generation, transport and recombination, and also account for the mesoscale ferroelectricity by incorporating domains with polarization, P, in 3D space, forming different polarization landscapes or microstructures. We show that the charge transport and recombination in the solar cell depends significantly on the polarization landscape viz. the orientation of domain boundaries and the size of domains. While the microstructure with highly-ordered polarized domains can lead to efficient charge transport in the device, evidenced by high fill factor (FF) and short-circuit current (JSC), the aforementioned ordering of domains is unlikely to occur in actual devices. In the case of the microstructure with random correlated polarization in domains, a realistic scenario, we find indication of the existence of channels for efficient charge transport in the device which leads to lowering of charge recombination as evidenced by the high FF. However, the high open-circuit voltage (VOC), which is typical of high performance perovskite solar cells is unlikely to be explained by the presence of ferroelectric polarization in the perovskite.
5:30 PM - EP3.5.10
Influence of Capacitive Effect and Ion Migration on the J-V Hysteresis Behaviour in Perovskite Solar Cells
Bo Chen 1,Mengjin Yang 2,Xiaojia Zheng 1,Juan Bisquert 3,Germa Garcia-Belmonte 3,Kai Zhu 2,Shashank Priya 1
1 Virginia Tech Blacksburg United States,2 National Renewable Energy Laboratory Golden United States3 Universitat Jaume I Castello Spain
Show AbstractIn past five years, perovskite solar cells based on organometal halide perovskite have been extensively investigated and shown to exhibit excellent photovoltaic performance. However, it has been widely recognized that photovoltaic measurement in perovskite solar cell depends on the speed of the voltage scan (hysteretic photocurrent density-voltage (J-V) behaviour), and also on history of voltage conditioning. To date, the origin of the J-V hysteresis behaviour is still under debate, and it has been proposed to originate from the capacitive effect due to giant photo-induced dielectric permittivity, dynamic charge trapping and de-trapping process, or band bending due to the ion migration and ferroelectric polarization. The presence of large capacitance at low frequency in perovskite solar cells has been observed. However, capacitive currents in operating conditions under one sun illumination have not been conclusively demonstrated. In addition, there is considerable evidence that the hysteresis phenomena and bias pre-treatment dependence of the J-V curves cannot solely be ascribed to capacitive response. These phenomena must be related to a strong modification of the photovoltaic mechanism very likely associated to the ion drift induced by photovoltage or polarization. In this study, we find that the varying responses of perovskite solar cells can be attributed to a dual cause. First, the capacitive effect associated with electrode polarization provides a slow transient non-steady-state photocurrent that modifies the J-V response. In addition, the ion-migration induced modification of interfacial barriers can modulate the charge collection efficiency so that it causes a pseudo-steady-state photocurrent that changes according to previous voltage conditioning. The formation of non-steady-state photocurrent and J-V hysteresis is dominated by the capacitive effect. The timescale for the decay of capacitive current is on the order of second, while the slow redistribution process of mobile ions under electric field requires several minutes.
5:45 PM - EP3.5.11
Elucidating Fast Recombination in Low Temperature Phase of CH3NH3PbClxI1-x Perovskite Thin Films Synthesized Using Continuous Liquid Interface Propagation
Som Sarang 1,Hidetaka Ishihara 1,Vincent Tung 1,Sayantani Ghosh 1
1 University of California Merced Merced United States,
Show AbstractOrganic-inorganic hybrid perovskites have been a major area of research due to their high performance and fast improving power conversion efficiency. Here, we report the electrohydrodynamically assisted continuous liquid interface propagation technique as a scalable, general, and yet versatile nano-manufacturing route toward synthesizing high quality thin films in a short time. This strategy makes use of a phenomenon called nanomarangoni effect to self-assemble emulsion droplets that are electro sprayed onto the substrate initiating a three-stage process of coalescence, spreading, and merging, thus optimizing thin film morphology upon deposition without the needs for additional engineering steps. This technique can lead to large scale production of perovskite printing technology for photovoltaic applications. In order to improve its performance as an active material in thin film solar cells grown using CLIP, it is important to understand the underlying physics governing its opto-electronic properties. Photoluminescence (PL) measurements showed that CH3NH3PbClxI1-x undergo a phase transition from tetragonal to orthogonal phase on cooling down below 130K. These low temperature phases are associated with more than one spectral peak indicating multiple recombination routes. Temperature dependent time-resolved PL measurements at low temperature reveal recombination rates an order of magnitude larger compared to the high temperature tetragonal phase. Power dependent emission study of these films reveal the high temperature recombination processes to be primarily bimolecular, whereas the low temperature recombination is governed by excitons, leading to a faster recombination rate. A binding energy of 105 meV was calculated from PL for the high temperature phase, which could be an upper bound on binding energy as free charge carriers seem to be dominating the recombination process at higher temperatures. In order to understand how binding energy effects the transition of charge carriers from free charges to excitons with temperature, we simulate the fraction of free charge carriers for perovskite crystals having different binding energy, at different temperatures. These studies reveal a shift in the type of intrinsic charge carriers in different phases of perovksite thin films, indicating a possibility of use in new opto-electronic devices.
This work is supported in by National Science Foundation DMR-1056860 and ECC-1227034