Exciton Bohr radius of lead halide perovskites for photovoltaic and light-emitting applications
Abstract
Exciton Bohr radius (aB) and exciton binding energy (Eb) 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 aB and εrc (dielectric constant) based on the net exciton energy above the bulk band gap. It is estimated that aB under the dielectric confinement is substantially smaller than aB in the absence of dielectric confinement: 4.36 nm vs. 5.61 nm in the case of CH3NH3PbBr3. We attribute the enhanced aB to variations of εrc and the electron-hole correlation energy. We also develop a simple method of finding Eb based on the same net exciton energy. Using this, we attribute the well-known difference in Eb between organic bromide perovskites and iodide counterparts to εrc and explain that iodide perovskites are more suited than bromide counterparts in photovoltaic applications, which require smaller Eb for efficient charge-carriers transport.
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