Boosted Hydrogen Evolution via Photoinduced Hole Transfer in Molecular‐Level Organic Heterojunction under NIR Photon Excitation

Abstract The energy of sunlight is predominantly concentrated in near‐infrared (NIR) region, posing a paramount limitation for practical application of conventional photocatalysts. Organic semiconductors can offer NIR absorption and tunable energy levels simultaneously through molecular engineering, which presents great potential in solar‐driven catalysis. However, an individual organic semiconductor typically generates Frenkel excitons with large binding energy, hindering efficient electron‐hole separation. Herein, we develop molecular‐level heterojunction to suppress electron‐hole recombination, thereby achieving a boosted hydrogen (H 2 ) evolution reaction rate of 25.54 µmol h −1 (12.77 mmol h −1 g −1 ) under visible–near‐infrared (Vis–NIR) light. Surprisingly, heterojunction nanoparticles (NPs) comprising donor polymer PBDB‐T matched with an A‐D 1 ‐D 2 ‐D 1 ‐A type acceptor BTPT‐IC4F exhibit a promising external quantum efficiency of 6.3% at 730 nm. Transient absorption spectroscopy monitors effective extraction of photogenerated holes from the highest occupied molecular orbital (HOMO) of BTPT‐IC4F to the HOMO of PBDB‐T, while first‐principle calculations confirm the prolonged lifetime of excited BTPT‐IC4F due to efficient hole capture by the PBDB‐T phase. The outstanding performance of heterojunction NPs under NIR light is ascribed to strong hole transfer within the nanoparticle. This study provides valuable insights for designing molecular‐level organic heterojunction photocatalysts toward NIR light‐driven H 2 evolution and other potential reactions.