Hydrophilic conjugated polymer additives in fullerene-heterojunction photocatalytic systems for efficient photocatalytic hydrogen evolution

Abstract

Photocatalytic hydrogen evolution from water has been regarded as a green technology for solar energy storage. Fullerene and its derivatives are promising organic photocatalysts due to their isotropic transmission and high electron affinity. However, carrier transfers in fullerene derivatives are hindered by the short exciton diffusion length and lifetime. The heterojunction strategy has been proven to promote exciton separation and improve carrier transport in organic solar cells. Here, we designed and synthesized a hydrophilic conjugated polymer named P4EOBDT-TTE to serve as an additive in fullerene-heterojunction photocatalytic systems. The hydrophilic P4EOBDT-TTE can optimize the heterojunction morphology without requiring additional surfactants, promote charge transfer and enhance exciton dissociation. Using transient and operando photoinduced optical absorption spectroscopies on ps–s timescales, we found that effective exciton separation in the fullerene-heterojunction is achieved through Förster energy transfer. By rationally optimizing the addition ratio, the heterojunction photocatalytic system containing 5% P4EOBDT-TTE demonstrated optimal photocatalytic hydrogen evolution activity, reaching 164.32 mmol g⁻¹ h⁻¹, more than 30 times that of pure PC₆₁BM (5.35 mmol g⁻¹ h⁻¹) under the same test conditions (AM 1.5G, 100 mW cm⁻² illumination for 5 h), representing one of the highest efficiency for hydrogen evolution with an organic photocatalyst.