Efficient generation of remarkably long-lived charges in organic semiconductor heterojunction nanoparticles enables high photocatalytic efficiency

Abstract

There is a growing interest in developing organic semiconductor photocatalysts for the synthesis of solar fuels. Most organic photocatalysts rely on exciton dissociation by sacrificial reagents to drive charge separation. We demonstrate that organic semiconductor nanoparticle (NP) photocatalysts comprising the conjugated polymer PM6 matched with PCBM or Y6 electron acceptors can intrinsically generate remarkably long-lived reactive charges, which enable them to efficiently drive the H2 evolution reaction (HER). The optimized PM6:Y6 NPs achieved external quantum efficiencies (EQEs) of 1.0% to 5.0% at 400 to 900 nm and the optimized PM6:PCBM NPs achieved EQEs of 8.7% to 2.6% at 400 to 700 nm. Selective Pt photodeposition was observed on the PCBM domain in the PM6:PCBM NPs and its location was rationalized based on the location of photogenerated electrons in the heterojunction. Employing transient and operando photoinduced optical absorption spectroscopies on ps-s timescales, we find that the heterojunction structure in these NPs greatly enhances the generation of long-lived charges (ms-s timescale) even in the absence of electron/hole scavengers or Pt. The generation of such long-lived reactive charges is striking and opens potential applications for driving kinetically slow and technologically desirable oxidations, or in water splitting Z-schemes.

Keywords Organic semiconductor, Organic photocatalysts, PM6, PCBM, EQEs