Size-Dependent Hydrogen Evolution in Organic Photovoltaic Catalysts: Balancing Exciton Dissociation and Charge Transport

Organic photovoltaic nanoparticles, with their tunable light absorption and exceptional charge dynamics, have shown promising potential for solar-driven hydrogen evolution. However, the interplay between exciton dissociation and charge transport in these systems remains poorly understood, limiting the efficiency of energy conversion. Here, we reinterpret this challenge using size/composition-tunable PM6:Y6 nanoparticles synthesized via a miniemulsion method. The PM6:Y6 heterojunction, featuring strong visible-light absorption and type-II energy level alignment, effectively facilitates exciton dissociation and charge separation, as evidenced by pronounced photoluminescence quenching and size-dependent transient fluorescence decay. Notably, nanoparticles with an optimized diameter of 63.9 nm exhibited the highest hydrogen evolution rate (110.13 ± 39.25 mmol g-1 h-1) and enhanced photocurrent density, attributed to an optimal balance between donor-acceptor interfacial area and charge transport pathways. Our findings reveal that both nanoparticle size and internal phase distribution critically influence photocatalytic performance, with smaller particles favoring short charge transport distance and larger particles benefiting from phase uniformity. This work establishes a comprehensive structure-property relationship that paves the way for the rational design of organic photovoltaic catalysts for efficient solar-to-hydrogen conversion.