Exciton Bohr radius of lead halide perovskites for photovoltaic and light-emitting applications

TL;DR

This paper introduces a theoretical approach to accurately determine the exciton Bohr radius and binding energy in lead halide perovskites, revealing their dependence on dielectric properties and implications for photovoltaic and light-emitting applications.

Contribution

A new reliable theoretical method for simultaneously calculating exciton Bohr radius and dielectric constant in lead halide perovskites is proposed, enhancing understanding of their optoelectronic properties.

Findings

Dielectric confinement reduces a_B from 5.61 nm to 4.36 nm in CH3NH3PbBr3.

E_b differences between bromide and iodide perovskites are explained by dielectric constant variations.

Iodide perovskites are more suitable for photovoltaics due to smaller E_b.

Abstract

Exciton Bohr radius (a_B) and exciton binding energy (E_b) of metal halide perovskites are two prime quantities in their applications to both light-emitting diode displays and photovoltaic devices. We develop a reliable theoretical method of simultaneously finding a_B and {\epsilon}_r^c (dielectric constant) based on the net exciton energy above the bulk band gap. It is estimated that a_B under the dielectric confinement is substantially smaller than a_B in the absence of dielectric confinement: 4.36 nm vs. 5.61 nm in the case of CH3NH3PbBr3. We attribute the enhanced a_B to variations of {\epsilon}_r^c and the electron-hole correlation energy. We also develop a simple method of finding E_b based on the same net exciton energy. Using this, we attribute the well-known difference in E_b between organic bromide perovskites and iodide counterparts to {\epsilon}_r^c and explain that iodide perovskites are more suited than bromide counterparts in photovoltaic applications, which require smaller E_b for efficient charge-carriers transport.