Highly Efficient and Stable Dye-Sensitized Photoelectrochemical Cells via Cascade Charge Transfer

Dye-sensitized photoelectrochemical cells (DSPECs) have shown promise in artificial photosynthesis for water splitting, but they face obstacles such as low photocurrents (0.01–2.2 mA/cm²) and limited stabilities (0.01–2 h, maintaining over 90% of initial photocurrent) due to degradation/decomposition of dye-sensitized photoelectrodes, along with inefficient charge transfer processes in aqueous electrolytes forming adaptive junction. To overcome these fundamental issues, we developed a “cascade-type” dye-sensitized photoelectrode utilizing platinum-sputtered nickel foil to encapsulate both the dye-sensitized TiO₂ layer and redox mediator electrolyte. This buried junction design enables spatially controlled cascade charge transfer, highly effective photoconversion, and active water oxidation facilitated by Ni-based catalysts, all without undesirable current leakage. By conducting a comprehensive study involving three redox electrolytes and optimizing water oxidation catalysts, our best-performing photoelectrode achieves a photocurrent of 14.5 mA/cm², Faradaic efficiency of approximately 98%, and photostability of 30 h under AM 1.5G illumination.