Atomic Layer Deposition of Space-Efficient SnO2 Underlayers for BiVO4 Host-Guest Architectures for Photoassisted Water Splitting.

Bismuth vanadate (BiVO4 ) is promising for solar-assisted water splitting. The performance of BiVO4 is limited by charge separation for >70 nm films or by light harvesting for <700 nm films. To resolve this mismatch, host-guest architectures use thin film coatings on 3D scaffolds. Recombination, however, is exacerbated at the extended host-guest interface. Underlayers are used to limit this recombination with a host-underlayer-guest series. Such underlayers consume precious pore volume where typical SnO2 underlayers are optimized with 65-80 nm. In this study, conformal and ultrathin SnO2 underlayers with low defect density are produced by atomic layer deposition (ALD). This shifts the optimized thickness to just 8 nm with significantly improved space efficiency. The materials chemistry thus determines the dimension optimization. Lastly, host-guest architectures are shown to have an applied bias photon-to-charge efficiency of 0.71 %, a new record for a photoanode absorber prepared by ALD.