Effect of Film and Shell Thickness on the Quantum Efficiency of Solution-Processed WO 3 ‐BiVO 4 Core‐Shell Nanoporous Film Photoanodes

Nanoporous core-shell heterojunction metal oxide photoanodes demonstrate enhanced photoelectrochemical water splitting efficiency through improved light absorption, charge carrier separation at the heterojunction, and charge transport through crystalline cores. Here we present a scalable solution-processed synthesis of nanoporous WO 3 -BiVO 4 core-shell photoanodes. These achieve 3.8 mA/cm 2 photocurrents under 1 sun illumination with internal quantum efficiencies of 70-100%, representing a 3-9x increase over single component BiVO 4 -only or WO 3 -only photoanodes. Through the systematic investigation of experimental and modeled optical properties, photoelectrochemical performance, and quantum efficiencies across film and shell thicknesses, we identified key design principles for optimizing light absorption and charge carrier collection in nanoporous core-shell architectures using this WO 3 -BiVO 4 model system. This solution-processed route provides a versatile and scalable platform that can be applied to lower-bandgap shell materials for enhanced solar spectrum utilization and higher photocurrents.