Influence of crystal structure on charge carrier effective masses in BiFeO$_3$

TL;DR

This study investigates how different crystal structures of BiFeO$_3$ influence charge carrier effective masses, revealing structural factors that can be manipulated to improve photovoltaic efficiency.

Contribution

It provides a systematic analysis of structure-effective mass relationships in BiFeO$_3$, offering design principles for optimizing photovoltaic properties through crystal structure engineering.

Findings

Identification of a tetragonal phase with light charge carriers and high polarization

Explanation of structure-effect mass relationship via orbital character changes

Guidelines for manipulating crystal structures to enhance photovoltaic performance

Abstract

Ferroelectric-based photovoltaics have shown great promise as a source of renewable energy, thanks to their in-built charge separation capability, yet their efficiency is often limited by low charge carrier mobilities. In this work, we compare the photovoltaic prospects of various phases of the multiferroic material BiFeO$_3$ by evaluating their charge carrier effective masses using first-principles simulations. We identify a tetragonal phase with the promising combination of a large spontaneous polarisation and relatively light charge carriers. From a systematic study of the octahedral distortions present in BiFeO$_3$, we explain the relationship between structure and effective masses in terms of the changes to the orbital character and overlap at the band edges that result from changes in the geometry. The findings in this study provide some design principles to engineer desired effective masses in BiFeO$_3$ and similar materials through manipulation of their crystal structures in experimentally accessible ways.