BiVO Photoanode with NiVO Back Contact Interfacial Layer for Improved Hole-Diffusion Length and Photoelectrochemical Water Oxidation Activity.

The short hole diffusion length (HDL) and high interfacial recombination are among the main drawbacks of semiconductor-based solar energy systems. Surface passivation and introducing an interfacial layer are recognized for enhancing HDL and charge carrier separation. Herein, we introduced a facile recipe to design a pinholes-free BiVO photoanode with a NiVO back contact interfacial (BCI) layer, marking a significant advancement in the HDL and photoelectrochemical activity. The fabricated BiVO photoanode with NiVO BCI layer exhibits a 2-fold increase in the HDL compared to pristine BiVO. Despite this improvement, we found that the front surface recombination still hinders the water oxidation process, as revealed by photoelectrochemical (PEC) studies employing NaSO electron donors and by intensity-modulated photocurrent spectroscopy measurements. To address this limitation, the surface of the NiVO/BiVO photoanode was passivated with a cobalt phosphate electrocatalyst, resulting in a dramatic enhancement in the PEC performance. The optimized photoanode achieved a stable photocurrent density of 4.8 mA cm at 1.23 V, which is 12-fold higher than that of the pristine BiVO photoanode. Density Functional Theory (DFT) simulations revealed an abrupt electrostatic potential transition at the NiVO/BiVO interface with BiVO being more negative than NiVO. A strong built-in electric field is thus generated at the interface and drifts photogenerated electrons toward the NiVO BCI layer and photogenerated holes toward the BiVO top layer. As a result, the back-surface recombination is minimized, and ultimately, the HDL is extended in agreement with the experimental findings.