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

Laura Geronimo, Catarina G. Ferreira, Valentina Gacha, Dimitrios Raptis, Jordi Martorell, and Carles Ros (2024). Understanding the Internal Conversion Efficiency of BiVO4/SnO2 Photoanodes for Solar Water Splitting: An Experimental and Computational Analysis. ACS Applied Energy Materials, 7(5), 1792–1801. https://doi.org/10.1021/acsaem.3c02775

Abstract

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. Researchers found the internal absorbed photon-to-current efficiency (APCE) to be nonconstant. This follows a specific dependence of the internal charge separation and extraction processes 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.

The results obtained are not only useful for accurate incident photon-to-current efficiency (IPCE) prediction but also contribute significantly to the computational modeling of BiVO4 and other metal oxide photoanodes. In essence, this study establishes a novel method to determine the sample’s thickness by analyzing its IPCE, while simultaneously accounting for variations in internal APCE conversion. Furthermore, the observed improvement in fill factor and photogenerated voltage can be attributed to the incorporation of an intermediate SnO2 hole-blocking layer. Notably, this layer demonstrates a negligible optical effect yet plays a crucial role in enhancing charge separation and extraction, particularly for lower energetic wavelengths. Additionally, researchers employed a Mott-Schottky analysis to confirm a 90 mV shift in the flat-band potential, further validating the effectiveness of this approach. In summary, the findings of this study represent a significant advancement in the understanding and optimization of photoanode materials.

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BiVO4/SnO2 photoanodes