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 (PDI^2-*) 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 PDI^2-*. 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.