Bilayer Heterojunction‐Based Organic Photoanodes Improve the Stability of the Oxygen Evolution Reaction

ABSTRACT Employing organic semiconductors (OSs) for photoelectrochemical (PEC) solar‐driven water splitting represents a promising route for sustainable hydrogen production; however, OS‐based photoanodes remain limited by poor stability for the PEC oxygen evolution reaction. Here, a bilayer heterojunction (BiHJ) architecture, obtained through orthogonal solution processing of two separate OS layers, is developed to enhance both charge transfer and operational durability compared to conventional bulk heterojunction (BHJ) structures. The BiHJ photoanode achieves a remarkable photocurrent onset near 0 V RHE and retains 62% of its initial activity after 22 h under sacrificial conditions, whereas the BHJ counterpart fails within 6 h. Electrochemical impedance spectroscopy reveals reduced interfacial resistance and charge accumulation at the BiHJ/electrolyte interface, and grazing incidence wide‐angle X‐ray scattering and Fourier‐transform infrared spectrocopy analyses confirm that the enhanced structural order and chemical robustness mitigate O 2 ‐induced degradation. When integrated with a poly(triarylamine) hole‐transport layer and Li‐IrO x catalyst, the BiHJ photoanode performs water oxidation for >15 h with significantly improved stability compared to the BHJ device under high applied bias at pH 9. This work establishes a viable device‐engineering approach toward achieving efficient and durable organic photoanodes for integrated Z‐scheme PEC water splitting.