Suppressing Charge Carrier Recombination in Bulk Heterojunction Organic Photocatalyst via Improving Molecular Crystallinity and Reducing Electron‐Phonon Coupling for Efficient Hydrogen Evolution Reaction

ABSTRACT Organic semiconductor bulk‐heterojunction nanoparticles have emerged as promising photocatalysts, due to their strong visible absorption in the Vis–NIR region, excellent optical/electronic adjustability, and spatially abundant interfaces for charge carrier separation. However, organic semiconductors generally suffer from inferior crystallinity and high lattice's susceptibility to molecular vibrations, which leads to the localization of separated charge carriers and severe recombination in nanoparticles, limiting the further improvement of photocatalytic H 2 evolution rate. Herein, a methoxy‐functionalized electron acceptor, ITIC‐OMe, is developed and presents enhanced crystallinity, more compact molecular packing and weaker electron–phonon coupling, compared to the parent ITIC. This enables ZnTPP‐3O:ITIC‐OMe bulk‐heterojunction nanoparticles to afford more ordered molecular stacking, reduced charge transfer resistance, and inhibited charge back transfer for triplet state formation, thereby suppressing charge carrier recombination and facilitating charge transport to the nanoparticle surface for proton reduction. Consequently, the photocatalyst based on ZnTPP‐3O:ITIC‐OMe bulk‐heterojunction nanoparticles achieves an impressive hydrogen evolution rate up to 1017.7 mmol g −1 h −1 under AM 1.5G illumination, which is the record for organic photocatalysts so far. It highlights that suppressing charge carrier recombination via finely molecular design is a powerful route to enhance the photocatalytic H 2 evolution performance.