Impact of Cation Multiplicity on Halide Perovskite Defect Densities and Solar Cell Voltages

Abstract
Metal-halide perovskites feature very low deep-defect densities, thereby enabling high operating voltages at the solar cell level. Here, by precise extraction of their absorption spectra, we find that the low deep-defect density is unaffected when cations such as Cs+ and Rb+ are added during the perovskite synthesis. By comparing single crystals and polycrystalline thin films of methylammonium lead iodide/bromide, we find these defects to be predominantly localized at surfaces and grain boundaries. Furthermore, generally, for the most important photovoltaic materials, we demonstrate a strong correlation between their Urbach energy and open-circuit voltage deficiency at the solar cell level. Through external quantum yield photoluminescence efficiency measurements, we explain these results as a consequence of nonradiative open-circuit voltage losses in the solar cell. Finally, we define practical power conversion efficiency limits of solar cells by taking into account the Urbach energy.

Citation
Ledinský, M., Vlk, A., Schönfeldová, T., Holovský, J., Aydin, E., Dang, H. X., … De Wolf, S. (2020). Impact of Cation Multiplicity on Halide Perovskite Defect Densities and Solar Cell Voltages. The Journal of Physical Chemistry C. doi:10.1021/acs.jpcc.0c08193

Acknowledgements
The authors acknowledge the support of the Czech Science Foundation (Project No. 17-26041Y), Operational Programme Research, Development, and Education financed by the European Structural and Investment Funds and the Czech Ministry of Education, Youth and Sports (Project No. CZ.02.1.01/0.0/0.0/16_019/0000760SOLID21 and CzechNanoLab Research Infrastructure LM2018110). E.A., H.X.D., and S.D.W. acknowledge financial support under Award No. OSR-CARF URF/1/3079-33-01 by King Abdullah University of Science and Technology (KAUST). J.V. acknowledges support from the Charles University Research Centre (UNCE/SCI/010).

Publisher
American Chemical Society (ACS)

Journal
The Journal of Physical Chemistry C

DOI
10.1021/acs.jpcc.0c08193

Additional Links
https://pubs.acs.org/doi/10.1021/acs.jpcc.0c08193

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