Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP20)
DOI: https://doi.org/10.29363/nanoge.iperop.2020.002
Publication date: 14th October 2019
The incorporation of cesium (Cs) and rubidium (Rb) ions into multiple-cation mixed lead halide perovskites increases their photovoltaic performance. In this study, the reasons for the performance increase are investigated by a set of steady-state and transient spectroscopy techniques. Analyzing the band edge absorption using Elliott’s model shows that the Cs/Rb-ion incorporation increases the band gap, while the excitonic binding energies remain low, in the range of a few milli-electronvolts. Low Urbach energies determined by photothermal deflection spectroscopy suggest optimized microstructures upon Cs/Rb incorporation. The charge carrier recombination dynamics indicate that Cs/Rb-incorporation reduces not only the first-order (trap-assisted) recombination, but also the second-order recombination in these perovskite films. Upon excitation, carrier density-induced broadening of the photo-bleaching following the Burstein-Moss model is observed and effective carrier masses are determined to be in the range of a few tenths of the electron rest mass, explaining the excellent charge carrier mobilities of these perovskite films. Sub-picosecond hot carrier cooling is observed, indicating a strong charge-phonon coupling. Our results unfold the impact of cesium/rubidium incorporation on the photophysics of multiple-anion lead halide perovskites and provide guidelines for future material engineering and device design.