Bias‐Free Highly Efficient and Stable Dye‐Sensitized Photoelectrochemical Cells via Cascade Charge Transfer

Abstract Dye‐sensitized photoelectrochemical cells hold promise for artificial photosynthesis but face challenges such as low photocurrents and limited stability. To address these limitations, a cascade‐type dye‐sensitized photoelectrode is developed by encapsulating a dye‐sensitized TiO 2 layer and redox mediator within platinum‐sputtered nickel foil. This buried‐junction design enables spatially controlled cascade charge transfer, featuring effective photoconversion and Ni‐catalyzed water oxidation, while suppressing undesirable recombination current leakage. Through a comprehensive study involving the selection of redox mediators and water oxidation catalysts, the best‐performing photoelectrode for water splitting achieves a photocurrent of 14.0 mA cm −2 at 0.72 V vs. reversible hydrogen electrode (RHE), a Faradaic efficiency of 98%, and photostability of 30 hours. Moreover, the versatility of our design extends to bias‐free H 2 O 2 production, achieving a photocurrent density of 7.83 mA cm −2 , a Faradaic efficiency of 92.2%, and a record‐high solar‐to‐fuel efficiency of 4.15% (2.13 µmol min −1 cm −2 ), with photostability of 150 hours.