Improving Charge Transfer Beyond Conventional Heterojunction Photoelectrodes: Fundamentals, Strategies and Applications

Abstract Photoelectrochemical (PEC) cells are regarded as a promising approach to convert sunlight to chemical fuels, whereas the serious photo‐induced charge recombination of the semiconductor photoelectrode hinders its solar conversion efficiency. Over the past few decades, designing and constructing heterojunction photoelectrodes via thermodynamically favorable charge transfer have been proven to be effective in boosting photo‐induced charge separation. However, the conventional heterojunction construction strategy generally introduces incompatible, nonconformal, or defective interfaces, leaving considerable room to improve the thermodynamically favorable charge transfer efficiency in the heterojunction photoelectrodes. To compensate for the unsatisfied charge transfer efficiency, some novel strategies, such as grain boundary engineering, band gap engineering, field‐effected engineering, etc., are adopted to provide additional charge transfer driving force, which significantly improves the charge transfer efficiency. In this review, these novel strategies are discussed beyond the conventional heterojunction construction, and the prospects for the development and applications of heterojunction photoanodes are also proposed.