Quasi-Large Hole Polarons in BiVO4-Implications for Photocatalysis and Solar Energy Conversion

TL;DR

This paper reveals that BiVO4 forms quasi-large hole polarons with high mobility, which explains its effectiveness as a photocatalyst and suggests phonon tuning as a strategy for improved solar energy conversion.

Contribution

The study demonstrates the existence of quasi-large hole polarons in BiVO4 using first-principles calculations, challenging the typical small polaron model and offering new insights for material design.

Findings

BiVO4 forms quasi-large hole polarons with ~2 nm radius.

These polarons have high mobility and are stabilized by acoustic phonons.

Large polarons contribute to BiVO4's superior photocatalytic properties.

Abstract

Bismuth vanadate (BiVO4 BVO) is a promising photocatalyst for solar energy conversion, but its efficiency is limited by small polaron formation. However, some physical properties of BVO deviate from typical small polaron behavior. Using the state-of-the-art first-principles calculations, we demonstrate that BVO forms a quasi-large hole polaron with a radius around 2 nm, resembling free carriers with high mobility. This polaron is stabilized primarily by acoustic phonon modes, creating a shallow trap state near the valence band maximum, which prolongs its lifetime. Simultaneously, it retains a redox potential comparable to that of free carriers. We propose that such large polarons explain the superior properties of BVO and other transition metal oxide photocatalysts. Tuning phonon modes to stabilize large polarons offers a promising strategy for designing materials with enhanced solar energy conversion efficiency.