Understanding the Internal Conversion Efficiency of BiVO₄/SnO₂ Photoanodes for Solar Water Splitting: An Experimental...

This work aims to understand the spin-coating growth process of BiVO₄ photoanodes from a photon absorption and conversion perspective. BiVO₄ layers with thicknesses ranging from 7 to 48 nm and the role of a thin (<5 nm) SnO₂ hole-blocking layer have been studied. The internal absorbed photon-to-current efficiency (APCE) is found to be nonconstant, following a specific dependence of the internal charge separation and extraction on the increasing thickness. This APCE variation with BiVO₄ thickness is key for precise computational simulation of light propagation in BiVO₄ based on the transfer matrix method. Results are used for accurate incident photon-to-current efficiency (IPCE) prediction and will help in computational modeling of BiVO₄ and other metal oxide photoanodes. This establishes a method to obtain the sample's thickness by knowing its IPCE, accounting for the change in the internal APCE conversion. Moreover, an improvement in fill factor and photogenerated voltage is attributed to the intermediate SnO₂ hole-blocking layer, which was shown to have a negligible optical effect but to enhance charge separation and extraction for the lower energetic wavelengths. A Mott-Schottky analysis was used to confirm a photovoltage shift of 90 mV of the flat-band potential.