Abstract
Abstract Photoactive tungsten oxide-based coatings were fabricated via a liquid-phase spin-coating method, with the addition of commercial TiO2 powder to make a composite. TiO2-added WO3 thin-film photoanodes (WO3–TiO2 composite) were investigated to identify the optimal concentration level for an enhanced photoelectrochemical performance. In the composite sample WO3–TiO2-(20%), TiO2 integrates into WO3, forming a heterojunction network that preserves crystallinity, improves charge separation, and accelerates charge transport. Further increasing the TiO2 concentration promotes particle agglomeration, increases the contribution of the wide band gap TiO2 phase, and consequently leads to band gap widening, reduced visible-light absorption, and less efficient charge transfer. The WO3–TiO2(20%) composite exhibits the best energy alignment, fastest interfacial kinetics, and highest photocurrent. This work demonstrates a novel, facile, solution-processed, and reproducible spin-coating route to explore the critical TiO2 concentration threshold in the WO3–TiO2 heterojunctions.