Tuning ferroelectric photovoltaic performance in R3c-CuNbO₃ through compressive strain engineering: a...

Most ferroelectric oxides exhibit relatively wide bandgaps, which pose limitations on their suitability for photovoltaics application. CuNbO₃ possesses potential ferroelectric properties with an R3c polar structure that facilitate the separation of charge carriers under illumination, promoting the generation of photovoltaic effects. The optical and ferroelectric properties of R3c-CuNbO₃, as well as the effect of strain on the properties are investigated by first-principles calculation in this paper. The calculated results indicate that R3c-CuNbO₃ 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 CuNbO₃, contributing to the efficient absorption of visible light. The bandgap of CuNbO₃ 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 CuNbO₃ are driven by the Nb-O bond interactions, which are not significantly weakened by the compressive strain. CuNbO₃ 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.