Heterogeneous Doping to Improve the Performance of Thin-Film Hematite Photoanodes for Solar Water Splitting

Ti-doped, undoped, and Zn-doped hematite (α-Fe 2 O 3 ) thick (∼1 μm) films were found to be n-type, weak n-type, and p-type, respectively. Heterogeneous doping profiles were generated in 30 nm thick hematite stacks on F:SnO 2 -coated glass substrates with 25 nm thick SnO 2 underlayers in order to investigate the effect of different doping profiles on photoelectrochemical performance and compare with homogeneously doped counterpart photoelectrodes. Among the homogeneously doped photoelectrodes, the Ti-doped sample displayed the highest plateau photocurrent but also the highest onset potential, whereas the Zn-doped one had the lowest onset potential and the lowest plateau photocurrent. Heterogeneously doped photoelectrodes displayed both high plateau photocurrent and low onset potential, with the highest performance achieved for the specimen with Ti-doped, undoped, and Zn-doped layers at the bottom, center, and top parts of the stack, respectively. This demonstrates the potential of heterogeneous doping to improve the performance of hematite photoelectrodes for solar water splitting.