Impact of Cesium/Rubidium Incorporation on the Photophysics of Multiple‐Cation Lead Halide Perovskites

by Yajun Gao, Kai Wang, Mingcong Wang, Jafar I.Khan, Ahmed Balawi, Wenzhu Liu, Stefaan De Wolf, Frédéric Laquai
Full Paper Year: 2020

Bibliography

Gao, Y., Wang, K., Wang, M., Khan, J.I., Balawi, A., Liu, W., Wolf, S.D. and Laquai, F. (2020), Impact of Cesium/Rubidium Incorporation on the Photophysics of Multiple‐Cation Lead Halide Perovskites. Solar RRL

Extra Information

This work, published in Solar RRL,  presents a detailed study of the photophysics of multiple‐cation mixed halide lead perovskites and develops a concise picture of the impact of cesium/rubidium incorporation on the photophysics and device performance.

Abstract

Incorporating cesium (Cs) or rubidium (Rb) cations into multiple‐cation lead mixed‐halide perovskites (FA0.83MA0.17Pb(I0.83Br0.17)3) increases their photovoltaic performance. In this study, the fundamental photophysics of perovskites are investigated by steady‐state and transient optical spectroscopy and the reasons for the performance increase are revealed. Cs/Rb‐cation incorporation slightly increases the bandgap, while exciton binding energies remain in the range of a few meV. Urbach energies are reduced, suggesting improved perovskite microstructure upon Cs/Rb incorporation. Carrier density‐induced broadening of the photo‐bleaching following the Burstein‐Moss model is observed, and the effective carrier masses are determined to be a few tenths of the electron rest mass. From fits of the high‐energy tail of the perovskite's photo bleach to Boltzmann's distribution, sub‐picosecond hot carrier cooling is revealed, implying strong carrier‐phonon coupling. Importantly, the charge carrier recombination dynamics indicate that Cs/Rb‐incorporation reduces both the first‐order (trap‐assisted) and the second‐order (radiative) recombination, which appears to be the main reason for the observed performance increase upon Cs/Rb‐cation incorporation. Overall, this work presents a detailed study of the photophysics of multiple‐cation mixed halide lead perovskites and develops a concise picture of the impact of cesium/rubidium incorporation on the photophysics and device performance.

Keywords

carrier cooling carrier dynamics halide perovskites ultrafast spectroscopy