Sub-unit-cell disorder and intensified band-to-band transitions in halide perovskites from first-principles
David Egger a
a Department of Physics, Technical University Munich, Germany, James-Franck-Str. 1, Garching, Germany
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Invited Speaker, David Egger, presentation 120
Publication date: 20th April 2022

Halide perovskite (HaP) materials have attracted great scientific interest in the past decade, which is in part because of their unique combination of properties. These systems show various fascinating physical properties revolving around their apparent electronic-structure and optical characteristics, which are concurrent with finite-temperature vibrational properties that are very unusual for technologically useful semiconductors and demand explanation. Here, I will present our most recent theoretical findings obtained by molecular dynamics based on density-functional theory for the all-inorganic, cubic CsPbBr3. It will be shown that motions of neighboring Cs-Br atoms interlock such that most likely Cs-Br distances are significantly shorter than what is inferred from an ideal cubic structure. The dynamic Cs-Br coupling coincides with shallow potential wells for anharmonic Br motions occurring within locally and dynamically disordered energy landscapes. These Br motions are found to occur preferentially perpendicular to the Pb-Br-Pb bonding axis, which leads to a rapid rise in the joint density of states. This is a favorable feature for photovoltaics, since it implies sharp optical absorption profiles.

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