Regensburg 2025 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 1: Perovskite and Photovoltaics I (joint session HL/KFM)
HL 1.7: Vortrag
Montag, 17. März 2025, 11:15–11:30, H13
The Effect of Overdamped Phonons on the Fundamental Band Gap of Perovskites — •Xiangzhou Zhu and David A. Egger — Physics Department, TUM School of Natural Sciences, Technical University of Munich, 85748 Garching, Germany
Different from conventional semiconductors, halide perovskites (HaPs) exhibit unique anharmonic fluctuations that strongly influence optoelectronic properties. Recent studies have shown that in specific temperature regimes, the strong phonon-phonon interactions in HaPs lead to overdamped phonons, where vibrational lifetimes drop below one oscillation period. However, the relationship between these overdamped phonons and atomic fluctuations, as well as their impact on optoelectronic properties, are not fully understood. Here, using molecular dynamics (MD) simulations and augmented stochastic Monte Carlo methods that account for phonon renormalization and imaginary modes, we contrast the band gap behavior of two anharmonic perovskite materials, SrTiO3 and CsPbBr3, of which only the latter exhibits overdamped phonons.[1] Our results show that the overdamped phonon dynamics in CsPbBr3 drive slow atomic fluctuations that are not adequately captured by conventional phonon quasiparticle descriptions. Importantly, we show that these overdamped phonon lead to significant renormalization of the band gap. Our work disentangles the consequences of anharmonic effects on the optoelectronic properties and electron-phonon interactions in perovskites.
[1] Zhu, X. & Egger, D. A. arXiv:2406.05201 (2024).
Keywords: Overdamped phonons; first-principles; molecular dynamics; band gap renormalization; perovskites