Nonequilibrium Deposition in Epitaxial BiVO₄ Thin Film Photoanodes for Improving Solar Water Oxidation Performance

To improve the photoelectrochemical performance of photoelectrodes, various modifications such as the doping of electron donors, morphology control, and adoption of catalysts have been widely implemented, among which the formation of type-II heterojunctions has been recognized as an effective method to significantly improve the charge transport efficiency of photoelectrodes. In this regard, we report on an in situ high-quality epitaxial BiVO4/Bi4V2O11 type-II heterojunction thin-film photoanode fabricated by using pulsed laser deposition on the basis of only one BiVO4 ceramic target using the transition between BiVO4 and Bi4V2O11 crystalline phases. Herein, for the first time, we report on the structural and chemical transition between monoclinic BiVO4 (010) and orthorhombic Bi4V2O11 (001) crystalline phases by simply controlling the oxygen partial pressure. Subsequently, the growth of epitaxial BiVO4/Bi4V2O11 heterojunction thin film is achieved by controlling only the oxygen partial pressure based on band alignment. At 1.23 VRHE, the photocurrent density of heterojunction BiVO4/Bi4V2O11 structure is also significantly higher than that of the epitaxial BiVO4 thin film owing to the effective charge transfer of the Bi4V2O11 thin film. This study strongly suggests that the nonequilibrium deposition of epitaxial BiVO4 thin films can propose a new paradigm in the structural design of photoanodes.