Michael Saliba, Adolphe Merkle Institute
Antonio Abate, Helmholtz Berlin
Juan-Pablo Correa-Baena, Massachusetts Institute of Technology
Laura Herz, University of Oxford
ET04.01: Interfaces I
Monday PM, November 26, 2018
Hynes, Level 3, Room Ballroom C
8:00 AM - *ET04.01.01
Healing Defects of Perovskite and Improving Efficiency of Solar Cells by Over 900% Through a New Post-Device Ligand-Induced Modification
Wallace Choy1,Hong Zhang1
University of Hong Kong1Show Abstract
While perovskite solar cells (PVSCs) have drawn intense attention due to their high solar-to-power conversion efficiency (PCE), their practical application is hampered by the poor long-term stability against moisture. Although strategies have been reported to solve this issue, they are introduced during core-device fabrication processes which will increase the risk of introducing unexpected impurities during the fabrication.
In this work, we propose a new scheme of ligand-induced post-device (LPD) modification of perovskite on completely fabricated devices at room temperature to simultaneously improve the performance and stability of PVSCs . The ligand vapors will induce chemical modification in the selected lateral regions particularly that of perovskite layer which prevent the diffusion of water molecules into the protected active perovskite region for enhancing PVSC stability. This post-device treatment could also passivate the surface defects of perovskites in active region for improving the PVSC performance. Interestingly, this LPD modification strategy shows a special ‘stitching effect’, namely repairing the as-fabricated ‘poor devices’ by healing the defects of perovskite in the operation region and significantly improve PCE by over 900%. The work greatly improves the production yield of PVSCs and their module performance as well as the reduction of lead-waste. It should be noted that the off-the-shelf treatment, completely separated from the fabrication process of common perovskite devices, provides a general strategy to improve the stability of different completed perovskite devices (e.g. solar cells, light-emitting diodes, and photodetectors) without introducing any undesirable impurities during device fabrication.
 H. Zhang, X. Ren, X. Chen, J. Mao, J. Cheng, Y. Zhao, Y. Liu, J. Milic, W.J. Yin, M. Grätzel, W.C.H. Choy*, "Improving the stability and performance of perovskite solar cells via off-the-shelf post-device ligand treatment", Energy & Environmental Science, 2018, DOI: 10.1039/C8EE00580J.
8:30 AM - ET04.01.02
Understanding the Role of Surfaces on Halide Segregation in Mixed-Anion Perovskites
Rebecca Belisle1,Kevin Bush1,Luca Bertoluzzi1,Aryeh Gold-Parker1,Michael Toney1,Michael McGehee1
Stanford Univ1Show Abstract
Photo-induced halide-segregation currently limits the perovskite chemistries available for use as high bandgap semiconductors for tandem solar cells. This is particularly problematic for perovskite-perovskite tandems, where semiconductors with bandgaps in excess of 1.8 eV are needed for optimal pairing with the low-bandgap tin-rich perovskites. And while the problem of halide-segregation is well documented in the literature, strategies to circumvent this problem are largely lacking. In this study we present a new method for hindering this process – surface modifications. By varying the surface chemistry of mixed-anion perovskites and monitoring the evolution of their photoluminescence and X-ray diffraction patterns under illumination, we link changes in the perovskite surface to changes in the rate of halide segregation. We observe that we can both reduce non-radiative recombination and dramatically slow the onset of halide segregation by applying specific post-deposition surface treatments to CH3NH3PbI2Br films. Additionally we demonstrate that the surface sensitivity of halide segregation extends to perovskite/selective contact interfaces as well, and that halide segregation is suppressed at specific perovskite/selective contact heterojunctions. Finally, by using these observations and an in depth knowledge of the perovskite surface chemistry, we present a model by which tuning surface chemistry can prevent halide segregation in the bulk of the perovskite. In short, we propose carrier trapping at perovskite surfaces as the driver for halide migration and subsequent halide segregation, and that by reducing the trapping at surface states with targeted surface treatments this process can be abated if not completely stopped. Overall, this work presents both a deeper understanding of the halide-segregation process in perovskites as well as a pathway towards stable high bandgap perovskites for high efficiency perovskite tandems.
8:45 AM - ET04.01.03
Effectively Transparent Top Contacts for Perovskite Solar Cells
Michael Kelzenberg1,Sisir Yalamanchili1,Thomas Russell1,Sophia Coplin1,Qin Yang1,Nina Vaidya1,Pilar Espinet Gonzalez1,Shujuan Huang2,Jincheol Kim2,Jianghui Zheng2,Anita Ho-Baillie2,Rebecca Saive3,Harry Atwater1
California Institute of Technology1,University of New South Wales2,University of Twente3Show Abstract
Perovskite solar cells are of great interest due to their potential for low cost and high performance. One of the challenges to attaining high photovoltaic conversion efficiency, particularly for large-area cells, is the tradeoff between the optical and electrical performance of the top contact. Because perovskite absorbers and selective electrode materials provide very little lateral conductivity for current collection, a transparent conductive oxide (TCO) such as indium tin oxide (ITO) must be used for the front contact. However, TCOs offer a tradeoff between transparency and conductivity, resulting in cells that slightly compromise both their short-circuit current density due to optical losses, and their fill factor due to resistive losses. A solution is to increase the density of the grid fingers such that thinner TCOs can be used; however, this increases the shading losses.
Recently, a method to produce effectively transparent front contact grids has been described (Adv. Optical Mater. 4 (10), 1470-1474 (2016); Photovoltaic Specialists Conference (PVSC) IEEE 43rd, 3612-3615, (2016); Sustainable Energy and Fuels, 1 (3), 593-598, (2017)). This approach yields a relatively dense array of high-aspect-ratio, triangular-shaped front contact fingers, in which light striking the metal is reflected towards the cell. We previously described the application of this technique to produce effectively transparent superstrates for perovskite solar cells, which based on optical absorption measurements, is