Dresden 2017 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 28: Poster: Fundamentals of Perovskite Photovoltaics (joint session CPP, DS, HL)

HL 28.20: Poster

Montag, 20. März 2017, 18:30–21:00, P1A

Temperature-dependent optical spectra of (CH₃NH₃)PbBr₃ single-crystals cleaved in ultrahigh vacuum — •Oskar Schuster¹, Max Wilhelm¹, Daniel Niesner¹, Ievgen Levchuk², Andres Osvet², Shreetu Shrestha², Miroslaw Batentschuk², Christoph Brabec^{2, 3}, and Thomas Fauster¹ — ¹Lehrstuhl für Festkörperphysik, FAU Erlangen-Nürnberg, Staudtstr. 7, D-91058 Erlangen, Germany — ²I-MEET, Department of Materials Science and Engineering, FAU Erlangen-Nürnberg, Martensstr. 7, D-91058 Erlangen, Germany — ³ZAE Bayern, Haberstr. 2a, D-91058 Erlangen, Germany

Temperature-dependent optical spectroscopy determines basic properties like band gap, exciton binding energy, and direct or indirect character of the gap. Differences have been reported between freshly cleaved crystals compared to as-grown ones or thin films. We present an approach that determines the absorption of cleaved crystals from measured one-photon and two-photon induced photoluminescence spectra. The extracted low-temperature band gap and exciton binding energy of 22 meV are in excellent agreement with the ones determined from other techniques. The direct band gap increases with temperature at <200 K, and decreases at higher temperature. The behavior is well described by the Bose-Einstein model. The associated exciton binding energy decreases for temperatures >200 K. We find a second transition 60 meV (90 meV) below the direct gap in the orthorhombic (tetragonal) phase, consistent with a slightly indirect gap. Emission from this transition is significantly reduced after exposing the crystals to air.