Photo-induced oxygen vacancy formation and anomalous photoconductivity in solution-processed CoFe2O4 thin films

Abstract

Designing an optoelectronic device requires adequate information about the photo-response of the active material. Here, we have studied the optical and optoelectrical properties of the solution-processed inverse spinel structured CoFe2O4 (CFO) thin film and correlated it with the photovoltaic performance of CFO active material-based all-oxide solar cell. The optical absorption spectra of spin-coated CFO films show the existence of a direct bandgap of 2.64 eV with a maximum absorption coefficient >105/cm. A simple spin-coated CFO/TiO2p–n heterojunction shows an open circuit voltage of over 0.95 V under 1 sun illumination. However, photo-induced oxygen vacancy formation and the desorption of surface oxygen lead to additional electron generation and hole capture, respectively, in the p-type CFO, resulting in an anomalous photocurrent decay under white light illumination, resulting in a low short-circuit current density. This study provides a fundamental understanding of photo-carrier dynamics in solution-processed CFO thin films and apprehends the photophysics of designing spinel-ferrite-based optoelectronic devices.