Photovoltaic devices based on hybrid perovskite materials have exceeded 22% efficiency due to high charge-carrier mobilities and lifetimes. Properties such as photocurrent generation and open-circuit voltage are influenced by the microscopic structure and orientation of the perovskite crystals, but are difficult to quantify on the intra-grain length scale and are often treated as homogeneous within the active layer. Here, we map the local short-circuit photocurrent, open-circuit photovoltage, and dark drift current in state-of-the-art methylammonium lead iodide solar cells using photoconductive atomic force microscopy. We find, within individual grains, spatially correlated heterogeneity in short-circuit current and open-circuit voltage up to 0.6 V. These variations are related to different crystal facets and have a direct impact on the macroscopic power conversion efficiency. We attribute this heterogeneity to a facet-dependent density of trap states. These results imply that controlling crystal grain and facet orientation will enable a systematic optimization of polycrystalline and single-crystal devices for photovoltaic and lighting applications.
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This material is based on work supported by the National Science Foundation Graduate Research Fellowship under Grant No. (NSF DGE 1106400) and by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the US Department of Energy under Award Number DE-SC0004993. L.L. thanks the AvH foundation for financial support through the Feodor-Lynen program. D.Z. acknowledges support by the US Department of Energy, Office of Science, SBIR/STTR Program Office, under Award Number DE-SC0013212. A.W.-B., M.M., J.L. and S.Y.L. were supported by a DOE Early Career Grant. Work at the Molecular Foundry was supported by the US Department of Energy (DOE), Office of Basic Energy Sciences, Scientific User Facilities Division, under contract no. DE-AC02-05CH11231 and user proposal 4233. J.B.N., S.E.R.-L. and F.M.T. acknowledge support from the Laboratory Directed Research and Development Program at the Lawrence Berkeley National Laboratory under Contract No. DE-AC02-05CH11231.
The authors declare no competing financial interests.
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Leblebici, S., Leppert, L., Li, Y. et al. Facet-dependent photovoltaic efficiency variations in single grains of hybrid halide perovskite. Nat Energy 1, 16093 (2016). https://doi.org/10.1038/nenergy.2016.93
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