First principles calculations of the Shift Current Bulk Photovoltaic Effect in Ferroelectrics

TL;DR

This study uses first principles calculations to analyze the shift current mechanism in ferroelectric BaTiO$_3$ and PbTiO$_3$, revealing detailed relationships between electronic structure and photovoltaic response.

Contribution

It provides the first ab initio analysis of shift current in ferroelectrics, linking electronic structure features to photovoltaic response and challenging previous assumptions about polarization dependence.

Findings

Shift current is the dominant photovoltaic mechanism in BaTiO$_3$.

Photocurrent depends on asymmetric, covalent electronic states, not just polarization.

Results suggest applications in solar energy, photocatalysis, and sensors.

Abstract

We calculate the bulk photovoltaic response of the ferroelectrics BaTiO$_3$ and PbTiO$_3$ from first principles by applying "shift current" theory to the electronic structure from density functional theory. The first principles results for BaTiO$_3$ reproduce eperimental photocurrent direction and magnitude as a function of light frequency, as well as the dependence of current on light polarization, demonstrating that shift current is the dominant mechanism of the bulk photovoltaic effect in BaTiO$_3$. Additionally, we analyze the relationship between response and material properties in detail. The photocurrent does not depend simply or strongly on the magnitude of material polarization, as has been previously assumed; instead, electronic states with delocalized, covalent bonding that is highly asymmetric along the current direction are required for strong shift current enhancements. The complexity of the response dependence on both external and material parameters suggests applications not only in solar energy conversion, but to photocatalysis and sensor and switch type devices as well.