Evidence of Large Polarons in Photoemission Band Mapping of the Perovskite Semiconductor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>CsPbBr</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>
Michele Puppin, S. Polishchuk, Nicola Colonna, A. Crepaldi, Dmitry N. Dirin, Olga Nazarenko, Riccardo De Gennaro, G. Gatti, Silvan Roth, T. Barillot, Luca Poletto, R. Patrick Xian, Laurenz Rettig, Martin Wolf, Ralph Ernstorfer, Maksym V. Kovalenko, Nicola Marzari, M. Grioni, Majed Chergui
Abstract
Lead-halide perovskite (LHP) semiconductors are emergent optoelectronic materials with outstanding transport properties which are not yet fully understood. We find signatures of large polaron formation in the electronic structure of the inorganic LHP CsPbBr_{3} by means of angle-resolved photoelectron spectroscopy. The experimental valence band dispersion shows a hole effective mass of 0.26±0.02 m_{e}, 50% heavier than the bare mass m_{0}=0.17 m_{e} predicted by density functional theory. Calculations of the electron-phonon coupling indicate that phonon dressing of the carriers mainly occurs via distortions of the Pb-Br bond with a Fröhlich coupling parameter α=1.81. A good agreement with our experimental data is obtained within the Feynman polaron model, validating a viable theoretical method to predict the carrier effective mass of LHPs ab initio.