Tuning ferroelectric photovoltaic performance in R 3 c -CuNbO 3 through compressive strain engineering: a first-principles study.

Most ferroelectric oxides exhibit relatively wide bandgaps, which pose limitations on their suitability for photovoltaics application. CuNbO 3 possesses potential ferroelectric properties with an R 3 c polar structure that facilitate the separation of charge carriers under illumination, promoting the generation of photovoltaic effects. The optical and ferroelectric properties of R 3 c -CuNbO 3 , as well as the effect of strain on the properties are investigated by first-principles calculation in this paper. The calculated results indicate that R 3 c -CuNbO 3 possesses a moderate band gap to absorb visible light. The interaction of Cu-O and Nb-O bonds is considered to have a crucial role in the photovoltaic properties of CuNbO 3 , contributing to the efficient absorption of visible light. The bandgap of CuNbO 3 becomes smaller and the density of states near the conduction and valence bands becomes relatively uniform in distribution under compressive conditions, which improves the photoelectric conversion efficiency to 29.9% under conditions of bulk absorption saturation. The ferroelectric properties of CuNbO 3 are driven by the Nb-O bond interactions, which are not significantly weakened by the compressive strain. CuNbO 3 is expected to be an excellent ferroelectric photovoltaic material by modulation of compressive strain due to the stronger visible light absorption and excellent ferroelectric behavior.