LAUSR

Knowledge of the complex optical constants of the hybrid perovskite CsPbBr3 in thin films is essential for their applications in optoelectronic devices. In this paper, we measured the optical constants of a perovskite CsPbBr3 thin film deposited on an FTO substrate. We characterized the CsPbBr3 thin film by X-ray diffraction, photoluminescence emission, atomic force microscopy, scanning electron microscopy, and absorption spectra. Complex optical constants of the CsPbBr3 thin film were measured by spectroscopic ellipsometry and modeled by a Tauc–Lorentz formulation with seven oscillators. The observed interband transitions, which are positioned at 2.39, 3.44, and 3.85 eV, are denoted Ecp1, Ecp2 and Ecp3. We used critical point fitting of the second-derivative spectrum d2(E2e)/dE2 to analyze these spectral features. We assigned the origins of the three critical points and discuss their intrinsic mechanisms. These results indicate that interband transitions are governed by {PbBr6}4− octahedra, and small Cs+ ions affect the bandgap by breaking the octahedral packing symmetry. The simulated absorption coefficient agreed well with the experimental data.