Measuring the Exciton Binding Energy: Learning from a Decade of Measurements on Halide Perovskites and Transition Metal Dichalcogenides

Abstract

AbstractThe exciton binding energy (Eb) is a key parameter that governs the physics of many optoelectronic devices. At their best, trustworthy and precise measurements of Eb challenge theoreticians to refine models, are a driving force in advancing the understanding of a material system, and lead to efficient device design. At their worst, inaccurate Eb measurements lead theoreticians astray, sow confusion within the research community, and hinder device improvements by leading to poor designs. This review article seeks to highlight the pros and cons of different measurement techniques used to determine Eb, namely, temperature‐dependent photoluminescence, resolving Rydberg states, electroabsorption, magnetoabsorption, scanning tunneling spectroscopy, and fitting the optical absorption. Due to numerous conflicting Eb values reported for halide perovskites (HP) and transition metal dichalcogenides (TMDC) monolayers, an emphasis is placed on highlighting these measurements in an attempt to reconcile the variance between different measurement techniques. It is argued that the experiments with the clearest indicators are in agreement on the following values: ≈350–450 meV for TMDC monolayers between SiO2 and vacuum, ≈150–200 meV for hBN‐encapsulated TMDC monolayers, ≈200–300 meV for common lead‐iodide 2D HPs, and ≈10 meV for methylammonium lead iodide.