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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 27: Focus Session: When theory meets experiment: Hybrid halide perovskites for applications beyond solar II (joint session HL/CPP)
CPP 27.3: Vortrag
Montag, 16. März 2020, 16:00–16:15, POT 251
Looking beyond the surface: The band gap of bulk methylammonium lead iodide — Oskar Schuster1, Peter Wientjes1, Shreetu Shrestha2, Ievgen Levchuk2, Mykhailo Sytnyk3, Gebhard Matt2, Andres Osvet2, Miroslaw Batentschuk2, Wolfgang Heiss3, Christoph Brabec2, Thomas Fauster1, and •Daniel Niesner1 — 1Lehrstuhl für Festkörperphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Staudtstr. 7, 91058 Erlangen, Germany — 2Materials Science Department (I-MEET), FAU, Martensstrasse 7, 91058 Erlangen, Germany — 3Materials Science Department, FAU, Energy Campus Nürnberg, 90429 Nürnberg, Germany
Reported optical properties of lead halide perovskites as basic as the absorption onset and the band gap vary significantly. To unambiguously answer the question whether the discrepancies are a result of differences between bulk and "near-surface" material, we perform bulk-sensitive two-photon absorption with an information depth in the millimeter range on single crystals. In the application-relevant room-temperature tetragonal phase (170 K) we find a bulk band gap of 1.55±0.01 eV. Reference measurements on the surface-near region in a reflection geometry show excitonic transitions at 1.59±0.01 eV, consistent with the literature. The small band gap of the bulk material explains the extended infrared absorption of crystalline perovskite solar cells, the narrow bandwidth of crystalline perovskite photodetectors making use of the spectral filtering at the surface, and the low-energy bands which carry optically driven spin-polarized currents.