Influence of post-deposition annealing on the photoelectrochemical performance of CuBi2O4 thin films

Complex metal oxide semiconductors are promising candidates to be used as photoelectrodes in solar water splitting devices. One particular example is copper bismuth oxide (CuBi2O4), which is a p-type semiconductor with an ideal bandgap of 1.6–1.8 eV and suitable band positions. However, the performance has been reported to be limited by photocorrosion and the mismatch between its optical absorption and charge carrier transport properties. It has been shown that the former can be overcome by the deposition of protection layers, while the latter can be addressed by the modification of the bulk properties of the material. Here, we deposited thin films of CuBi2O4 using pulsed laser deposition (PLD). This results in high quality films, as evident from the internal quantum efficiency, which is comparable to the best-performing CuBi2O4 photoelectrodes. We investigate the bulk modification of the films by exploring post-deposition annealing treatment at various temperatures and oxygen partial pressures. These post-deposition annealing parameters influence the morphology of the films through the formation of aggregated particles/islands with higher crystallinity. The anneal treatment reduces bulk recombination in the film and increases the AM1.5 photocurrent by a factor of more than three. The influence of the high temperature post-deposition annealing treatment on other properties of CuBi2O4 (absorption, formation, and suppression of defects) is also discussed. This study underlines the importance of high temperature post-deposition annealing treatment in optimizing the performance of complex metal oxide photoelectrodes.