Switchable Ferroelectric Photovoltaic Effects in Epitaxial Thin Films of h-RFeO3 having Narrow Optical Band Gaps

TL;DR

This paper introduces switchable ferroelectric photovoltaic effects in narrow-bandgap h-RFeO3 thin films, demonstrating their potential for high-efficiency solar cells and optoelectronic devices due to their large polarization and switchability.

Contribution

It presents a novel class of ferroelectric photovoltaics using h-RFeO3 thin films with narrow band gaps, showing switchable effects and improved power conversion efficiency.

Findings

h-RFeO3 films have ~1.2 eV band gaps suitable for photovoltaics.

h-TmFeO3 thin film exhibits twice the PCE of BiFeO3.

Switchable photovoltaic effects dominate over internal field effects.

Abstract

Ferroelectric photovoltaics (FPVs) have drawn much attention owing to their high stability, environmental safety, anomalously high photovoltages, coupled with reversibly switchable photovoltaic responses. However, FPVs suffer from extremely low photocurrents, which is primarily due to their wide band gaps. Here, we present a new class of FPVs by demonstrating switchable ferroelectric photovoltaic effects using hexagonal ferrite (h-RFeO3) thin films having narrow band gaps of ~1.2 eV, where R denotes rare-earth ions. FPVs with narrow band gaps suggests their potential applicability as photovoltaic and optoelectronic devices. The h-RFeO3 films further exhibit reasonably large ferroelectric polarizations, which possibly reduces a rapid recombination rate of the photo-generated electron-hole pairs. The power conversion efficiency (PCE) of h-RFeO3 thin-film devices is sensitive on the magnitude of polarization. In the case of h-TmFeO3 (h-TFO) thin film, the measured PCE is twice as large as that of the BiFeO3 thin film, a prototypic FPV. We have further shown that the switchable photovoltaic effect dominates over the unswitchable internal field effect arising from the net built-in potential. This work thus demonstrates a new class of FPVs towards high-efficiency solar cell and optoelectronic applications.