Photo-physical properties of solution-processed CuFe₂O₄ thin films towards all oxide TiO₂/CuFe₂O₄ heterojunction photovoltaics

Finding low-cost, solution-processed, stable, and environmentally friendly materials that absorb visible light is the main challenge in designing optoelectronic devices such as photovoltaic (PV) cells. Spinel-structured p-type CuFe₂O₄ (CFO) is an environmentally stable, non-toxic complex oxide known for its superparamagnetic properties. Having a narrow bandgap with a high-absorption coefficient, it has been used for photocatalytic activities and photo-electrochemical water splitting. Here, we explore the feasibility of solution-processed CFO thin film as an absorber layer in n-p heterojunction PV cells. Spin-coated CFO thin film on a fluorine-doped tin oxide (FTO) coated glass substrate shows a single-phase spinel tetragonal crystal structure with an optical band gap of around 2 eV and a high absorption coefficient of 10⁵ cm⁻¹. A steady rise under illumination in the transient photocurrent response of the CFO films confirms its visible light sensitivity. The solution-processed all oxide TiO₂/CFO-based n-p heterojunction shows typical diode-like characteristics, and under 1 sun illumination, it shows a photovoltage over 430 mV and photocurrent density of 0.432 mA cm⁻². Hence, the studied optoelectronic properties of CFO thin films indicate the possibility of CFO as an active material in PV cells that further strengthens its multifunctionality.