An Integrated Metal‐Free Modification Method to Construct Efficient and Durable Bulk Heterojunction Photocathode for Solar Hydrogen Production

Polymer semiconductor with bulk heterojunction (BHJ) structure has attracted increasing attention to fabricate highly efficient photoelectrode for converting solar energy and water into hydrogen, thanks to its high photocurrent output and positive onset potential beyond 0.6 V. However, BHJ‐based photoelectrodes demonstrate poor anticorrosion against irradiation in aqueous environment, thus the photoelectrochemical (PEC) stability is a very intractable problem to solve. Herein, an inside and outside integrated modification method is developed to help BHJ‐based photocathode withstand PEC erosion during hydrogen production in acidic solution. The obtained BHJ (PBDB‐T:ITIC:PC71BM)‐based photocathode with surface carbon protective layer allows sustained and fast PEC hydrogen evolution (an average photocurrent density up to 13.5 mA cm−2) for a duration up to 15 h, which is among the best results of BHJ‐based photocathodes. The internal modification with fullerene derivative of PC71BM boosts the photogenerated electron transfer to balance against relative fast hole transfer, which largely alleviates electron accumulation and improves PEC intrinsic stability as a result. The surface carbon layer effectively resists the permeation of aqueous electrolyte without hindering interfacial charge transfer. This metal‐free protective method is very promising toward construction of highly robust BHJ‐based photoelectrodes for sustainable water splitting. An “inside and outside integrated” modification method is applied to construct by far the most efficient and durable organic bulk heterojunction (BHJ)‐based photocathode for hydrogen production. The incorporation of PC71BM with high electron mobility alleviates the charge accumulation in photocathode and boosts its intrinsic stability. The metal‐free modification by carbon plate physically resists against the electrolyte erosion without impeding charge transfer.