First-Principles Calculation of the Bulk Photovoltaic Effect in KNbO$_{3}$ and (K,Ba)(Ni,Nb)O$_{3-\delta}$

TL;DR

This study uses first-principles calculations to analyze the bulk photovoltaic effect in specific ferroelectric materials, revealing how structural factors influence photovoltaic performance and offering insights for designing better photovoltaic devices.

Contribution

It provides a systematic first-principles analysis of the BPVE in (K,Ba)(Ni,Nb)O$_{3- ext{ extdelta}}$ and KNbO$_{3}$, highlighting the effects of structural and compositional variations on photovoltaic efficiency.

Findings

(K,Ba)(Ni,Nb)O$_{3- ext{ extdelta}}$ has comparable BPVE to BiFeO$_{3}$ at lower photon energies.

Glass coefficient of (K,Ba)(Ni,Nb)O$_{5}$ can be 12 times larger than BiFeO$_{3}$.

Wavefunction nature and defect engineering significantly affect shift current yield.

Abstract

The connection between noncentrosymmetric materials' structure, electronic structure, and bulk photovoltaic performance remains not well understood. In particular, it is still unclear which photovoltaic (PV) mechanism(s) are relevant for the recently demonstrated visible-light ferroelectric photovoltaic (K,Ba)(Ni,Nb)O$_{3-\delta}$. In this paper, we study the bulk photovoltaic effect (BPVE) of (K,Ba)(Ni,Nb)O$_{3-\delta}$ and KNbO$_{3}$ by calculating the shift current from first principles. The effects of structural phase, lattice distortion, oxygen vacancies, cation arrangement, composition, and strain on BPVE are systematically studied. We find that (K,Ba)(Ni,Nb)O$_{3-\delta}$ has a comparable BPVE with that of the broadly explored BiFeO$_{3}$, but for a much lower photon energy. In particular, the Glass coefficient of (K,Ba)(Ni,Nb)O$_{5}$ in a simply layered structure can be as large as 12 times that of BiFeO$_{3}$. Furthermore, the nature of the wavefunctions dictates the eventual shift current yield, which can be significantly affected and engineered by changing the O vacancy location, cation arrangement, and strain. This is not only helpful for understanding other PV mechanisms that relate to the motion of the photocurrent carriers, but also provides guidelines for the design and optimization of PV converters.