Interfacial Engineered Perylene Diimide Sensitized Photocathode for Enhanced Photoelectrocatalytic Energy-Demanding Reduction Reactions

Dye‐sensitized photoelectrochemical cells (DSPECs) are emerging inexpensive devices for solar fuels production and chemical upgrading, yet their efficiency remains limited by poor photocurrent density especially in energy‐demanding reactions. Here, we introduce a molecularly engineered photocathode that integrates perylene diimides (PDI)—capable of consecutive photoinduced electron transfer (ConPET) to generate an excited state (PDI2−*) with potent reducing power—on a transparent conductive indium tin oxide nanoparticle (nanoITO) thin film substrate. By introducing an Al2O3 atomic layer via atomic layer deposition (ALD) onto the interface of PDI and nanoITO, the nonproductive back‐electron transfer (BET) was significantly suppressed by over 95%, as quantified by transient absorption spectroscopy, while preserving the exceptional photoredox activity of PDI2−*. This novel photocathode enables efficient activation of energy‐demanding reduction reactions requiring highly negative reduction potentials, exemplified by the dehalogenation of 4‐bromoacetophenone. This work demonstrates a novel approach for DSPECs, prioritizing interfacial control to unlock the potential of energy‐demanding photoredox transformations.