Temperature-Dependent Optical Band Gap in CsPbBr<sub>3</sub>, MAPbBr<sub>3</sub>, and FAPbBr<sub>3</sub> Single Crystals
Giovanni Mannino, Ioannis Deretzis, Emanuele Smecca, Antonino La Magna, Alessandra Alberti, Davide Raffaele Ceratti, David Cahen
Abstract
) by spectroscopic ellipsometry in the range of 1-5 eV while varying the temperature from 183 to 440 K. An extremely low absorption coefficient in the sub-band gap region was found, indicating the high optical quality of all three crystals. We extracted the band gap values through critical point analysis showing that Tauc-based values are systematically underestimated. The two structural phase transitions, i.e., orthorhombic-tetragonal and tetragonal-cubic, show distinct optical behaviors, with the former having a discontinuous character. The cross-correlation of optical data with DFT calculations evidences the role of octahedral tilting in tailoring the value of the band gap at a given temperature, whereas differences in the thermal expansion affect the slope of the band gap trend as a function of temperature.