Revealing the Impact of Cesium/Rubidium Incorporation on the Photophysics of Multiple-Cation Lead Halide Perovskites
Yajun Gao a, Kai wang a, mingcong wang a, Jafar Khan a, Ahmed Balawi a, Stefaan Wolf a, Frederic Laquai a
a King Abdullah University of Science and Technology (KAUST) - Saudi Arabia, 4700 King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP20)
Tsukuba-shi, Japan, 2020 January 20th - 22nd
Organizers: Michio Kondo and Takurou Murakami
Oral, Yajun Gao, presentation 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.

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