Enhanced Photocatalytic and Photovoltaic Performance Arising from Unconventionally Low Donor–Y6 Ratios

Abstract Development of both organic photovoltaics (OPVs) and organic photocatalysts has focused on utilizing the bulk heterojunction (BHJ). The BHJ promotes charge separation and enhances the carrier lifetime, but may give rise to increased charge traps, hindering performance. Here, high photocatalytic and photovoltaic performance is displayed by electron donor–acceptor (D–A) nanoparticles (NPs) and films, using the nonfullerene acceptor Y6 and polymer donor PIDT‐T8BT. In contrast to conventional D–A systems, the charge generation in PIDT‐T8BT:Y6 NPs is mainly driven by Y6, allowing a high performance even at a low D:A mass ratio of 1:50. The high performance at the low mass ratio is attributed to the amorphous behavior of PIDT‐T8BT. Low ratios are generally thought to yield lower efficiency than the more conventional ≈1:1 ratio. However, the OPVs exhibit peak performance at a D:A ratio of 1:5. Similarly the NPs used for photocatalytic hydrogen evolution show peak performance at the 1:6.7 D:A ratio. Interestingly, for the PIDT‐T8BT:Y6 system, as the polymer proportion increases, a reduced photocatalytic and photovoltaic performance is observed. The unconventional D:A ratios provide lower recombination losses and increased charge‐carrier lifetime with undisrupted ambipolar charge transport in bulk Y6, enabling better performance than conventional ratios. This work reports novel light‐harvesting materials in which performance is reduced due to unfavorable morphology as D:A ratios move toward conventional ratios of 1:1.2–1:1.