Ellipsometric study of the complex optical constants of a CsPbBr3 perovskite thin film

Knowledge of the complex optical constants of the hybrid perovskite CsPbBr 3 in thin films is essential for their applications in optoelectronic devices. In this paper, we measured the optical constants of a perovskite CsPbBr 3 thin film deposited on an FTO substrate. We characterized the CsPbBr 3 thin film by X-ray diffraction, photoluminescence emission, atomic force microscopy, scanning electron microscopy, and absorption spectra. Complex optical constants of the CsPbBr 3 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 E cp1 , E cp2 and E cp3 . We used critical point fitting of the second-derivative spectrum d 2 ( E 2 )/d E 2 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 {PbBr 6 } 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. Complex optical constants and interband transitions of a hybrid perovskite CsPbBr 3 thin film measured by spectroscopic ellipsometry.