Dresden 2020 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 61: Perovskite and photovoltaics III (joint session HL/CPP)

CPP 61.8: Talk

Wednesday, March 18, 2020, 11:45–12:00, POT 251

Anharmonicity, short-range correlated disorder, and small Urbach energies in halide perovskites — •Christian Gehrmann and David A. Egger — Department of Physics, Technical University Munich, 85748 Garching, Germany.

Halide perovskites (HaPs) are known to show complex nuclear dynamics and structural effects. But seemingly in contrast to this effects, a low amount of disorder is implied by measurements of small Urbach energies and sharp optical absorption edges. Using density functional theory (DFT) and DFT-based molecular dynamics, we calculated spatial correlations in the disorder potential induced for electronic states due to nuclear dynamics in representative HaPs [1]. We find sizeable anharmonicity in the nuclear vibrations and a dynamic shortening of correlations in the disorder potential: the motion of especially A-site and X-site ions are found to have an important impact on the length of spatial correlations in the disorder potential, such that they become as short as atomic bonds in the material. We explicitly establish that these short-range correlated disorder potentials lead to narrow band-energy distributions, which imply small Urbach energies. We conclude that effective collection of sunlight in HaP based photovoltaic devices, as indicated by small Urbach energies and sharp optical absorption edges, is facilitated by this mechanism.

[1] C. Gehrmann & D. A. Egger, Nat. Commun. 10, 3141 (2019).