The confusion about S-scheme electron transfer: critical understanding and a new perspective

Abstract

Charge separation is a crucial process that is closely related to the field of information and energy applications such as optoelectronics, photovoltaics, and artificial photosynthesis. The S-scheme electron transfer is widely used to regulate carrier separation due to its unique superiority. However, as our understanding of this field continues to evolve, there remain many controversial and ambiguous issues that are not well addressed. Focusing on the S-scheme electron transfer, this perspective delves into the reasons behind the confusion between the mechanisms of type-II and S-scheme transfer and clearly affords the theoretical criteria for the establishment of type-II transfer and S-scheme transfer. Considering the Fermi level alignment in a heterojunction is only applicable to the ideal situation, but not to the actual situation. The theory of Fermi level bending is further elaborated. To answer the question of whether the S-scheme driving force can be sustained, the phenomenon of Fermi level pinning is discussed intensively. Finally, the current problems and future development directions of S-scheme electron transfer are summarized and prospected.