Band gap tuning of solution processed ferroelectric perovskite BiFe1-xCoxO3 thin films

Abstract

Ferroelectric perovskite oxides are emerging as a promising photoactive layer for photovoltaic applications due to their very high stability and their alternative ferroelectricity-related mechanism for solar energy conversion that could lead to extraordi-narily high efficiencies. One of the biggest challenges so far is to reduce their band gap towards the visible while simultane-ously retaining ferroelectricity. To address these two issues, herein it is performed an elemental composition engineering of BiFeO3 by substituting Fe by Co cations, as means to tune the characteristics of the transition metal-oxygen bond. We demonstrate by solution processing the formation of epitaxial, pure phase and stable BiFe1-xCoxO3 thin films for x=0.3 and film thickness up to 100 nm. Importantly, the band gap can be tuned from 2.7 eV to 2.3 eV upon cobalt substitution while simultaneously enhancing ferroelectricity. As a proof of concept, non-optimized vertical devices have been fabricated and, reassuringly, the electrical photoresponse in the visible of the Co-substituted phase is improved with respect to the unsubsti-tuted oxide.