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.
Bibliographical noteKAUST Repository Item: Exported on 2020-12-17
Acknowledged KAUST grant number(s): OSR-CARF URF/1/3079-33-01
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_019/0000760SOLID21 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).