Photophysical properties and photoelectrochemical performances of sol-gel derived copper stannate (CuSnO3) amorphous semiconductor for solar water splitting application

Copper tin oxide, CuSnO3 (CSO), is an amorphous oxide semiconductor with a band-gap of 2.0-2.5 eV, and it is an attractive material for diverse applications such as transparent conducting oxides, transistors, and optoelectronic devices. In this study, we fabricated CSO thin films on fluorine-doped tin oxide (FTO)/glass substrates using a facile sol-gel process, and their optical properties, band structure and photoelectrochemical (PEC) properties were investigated using UV-Vis spectroscopy, photocurrent-density-potential (J-V) curves, electrochemical impedance spectroscopy, and Mott-Schottky analysis. The CSO film synthesized at 500 °C had an amorphous phase and a band gap of ~ 2.3 eV with n-type behavior, while the films synthesized at 550 °C and 600 °C had a phase mixture (SnO2 + CuO). We identified for the first time that the CSO film could be applied to photoelectrodes for photoelectrochemical water-splitting systems. Importantly, when combining the CSO with nanostructured WO3 film, i.e., the bilayer heterojunction of the a-CSO/WO3 showed enhanced PEC performances (cathodic shift of onset potential, increase of photocurrent generation and O2 evolution) compared to the pristine WO3 film.