An Excitonic Perspective on Low-Dimensional Semiconductors for Photocatalysis

Low-dimensional semiconductors provide a marvelous platform for pursuing versatile photocatalytic solar energy conversion. Compared with the bulk counterparts, low-dimensional semiconductors possess notable Coulomb-interaction-mediated excitonic effects arising from the reduced dielectric screening. As a consequence, excitons or bound electron-hole pairs, together with charge carriers, serve as the primary photoinduced energetic species. In terms of photocatalysis, exciton-based energy transfer establishes distinctly different mechanisms for energy utilization beyond the traditional carrier-based charge transfer. Moreover, owing to the relationships between excitons and charge carriers, excitonic effects play a crucial role in determining quantum yields of both exciton- and carrier-triggered photocatalytic reactions. The above unique features enable optimized low-dimensional semiconductor-based photocatalysis to be achieved by non-trivial excitonic regulation. In this Perspective, we attempt to provide an overview of the impacts of excitonic effects on low-dimensional semiconductor-based photocatalysis. By figuring out the differences between excitons and charge carriers in degrees of freedom like spin and orbital, we emphasize the importance of unique excitonic properties in photocatalytic energy conversion. We discuss the interplay between the excitonic and charge-carrier aspects in low-dimensional semiconductors and highlight the necessity of evaluating excitonic effects when dealing with both exciton- and carrier-triggered photocatalytic reactions. We further review recent achievements in regulating the excitonic properties of low-dimensional semiconductor-based photocatalysts. We conclude the Perspective with an eye toward the future challenges in the field.