Enhancing charge extraction in BiVO4 photoanodes by ZrCl4 treatment of SnO2 hole-blocking layers

• A ZrCl 4 treatment improves the effectiveness of SnO 2 as a hole-blocking layer in BiVO 4 photoanodes. • ZrCl 4 treatment significantly enhances the hole-blocking properties of SnO 2 . • This treatment results in a 37 % increase in photocurrent density at 1.23 V RHE and a 40 mV shift in the onset voltage. In the search for more efficient and sustainable photoelectrochemical devices, BiVO 4 is nowadays one of the best-performing photoanode material, with favourable band structure for water oxidation. However, BiVO 4 photoanodes face challenges such as poor charge transport and slow kinetics. To address these issues, SnO 2 films are commonly used as hole blocking layers, reducing recombination rate and enhancing charge lifespan and overall productivity. Yet, this method encounters problems like high defect concentrations at the SnO 2 /BiVO 4 interface and pinholes in the SnO 2 layer, which lead to charge recombination. In this study, we explore a ZrCl 4 treatment to improve the effectiveness of SnO 2 as a hole-blocking layer in BiVO 4 photoanodes. Our findings, supported by detailed optoelectronic characterization and continuous and modulated electrochemical analysis, reveal that ZrCl 4 treatment significantly enhances the hole-blocking properties of SnO 2 . This treatment results in a 37 % increase in photocurrent density at 1.23 V RHE and a 40 mV shift in the onset voltage, demonstrating a substantial improvement in overall photoanode efficiency.