High-energy optical transitions and optical constants of CH$_3$NH$_3$PbI$_3$ measured by spectroscopic ellipsometry and spectrophotometry

TL;DR

This study measures the optical constants of CH$_3$NH$_3$PbI$_3$ thin films using spectroscopic ellipsometry and spectrophotometry, identifying key optical transitions and providing data crucial for optoelectronic device design.

Contribution

It offers comprehensive optical constants and transition data for MAPbI$_3$, including additional transitions at higher energies, aiding in device modeling and material understanding.

Findings

Identified optical transitions at 1.58, 2.49, 3.36 eV

Detected additional transitions at 4.63 and 5.88 eV

Provided accurate optical constants over 0.73 to 6.45 eV

Abstract

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 is essential for engineering device architectures, which requires accurate optical data for the materials utilized. 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 CH$_3$NH$_3$PbI$_3$ (MAPbI$_3$) thin films over a photon energy range of 0.73 to 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 1.58, 2.49, 3.36 eV, but also additional transitions at 4.63 and 5.88 eV, which are observed in both SE and spectrophotometry measurements. This work provides important information relating to optical transitions and band structure of MAPbI$_3$, which can assist in the development of potential applications of the material.