High-Energy Optical Transitions and Optical Constants of CH3NH3PbI3 Measured by Spectroscopic Ellipsometry and Spectrophotometry

Optoelectronics based on metal halide perovskites (MHPs) have shown substantial promise, following more than a decade of research. For prime routes of commercialization such as tandem solar cells, optical modeling which requires accurate optical data for the materials utilized is essential for engineering device architectures. Additionally, a comprehensive understanding of the fundamental material properties is vital for simulating the operation of devices for design purposes. In this article, we use variable angle spectroscopic ellipsometry (SE) to determine the optical constants of CH3NH3PbI3 (MAPbI3) thin films over a photon energy range of 0.73–6.45 eV. We successfully model the ellipsometric data using six Tauc–Lorentz oscillators for three different incident angles. Following this, we use critical-point analysis of the complex dielectric constant to identify the well-known transitions at 1.59, 2.49, and 3.31 eV but also additional transitions at 4.39 and 5.65 eV, which are observed in both SE and spectrophotometry measurements. This work provides important information relating to optical transitions and the band structure of MAPbI3, which can assist in the development of potential applications of the material.