Visible-light absorption of indium oxide thin films via Bi3+ doping for visible-light-responsive photocatalysis

In2O3 is commonly used as a photocatalyst for hydrogen energy storage. However, it has the disadvantage of a large optical bandgap (3.7 eV), resulting in low absorption of visible light, which corresponds to 50 % of sunlight energy. Band engineering is an efficient method to add visible-light responsivity to wide-bandgap In2O3. In this study, the band engineering of In2O3 was performed by incorporating bismuth to obtain an intermediate band that could absorb visible light. Thin films of In2O3 doped with bismuth (IBO) were grown using mist chemical vapor deposition (CVD), and their optical properties were investigated. Transmittance measurements showed that the IBO thin film exhibited absorption in the visible light region of 400–700 nm, indicating that the introduction of bismuth created an intermediate band in the bandgap of In2O3. IBO thin films with platinum as a co-catalyst could almost completely degrade methylene blue under visible light (420 nm) irradiation for 72 h. Thus, the incorporation of bismuth into In2O3 via mist CVD and the strong absorption of visible light owing to its intermediate band were demonstrated. This study demonstrates that IBO thin films with large absorption in the visible-light region are promising materials for visible-light-responsive photocatalysts.