An organic semiconductor-based photocatalyst sheet for overall solar-driven water splitting

Abstract Splitting water into hydrogen and oxygen using sunlight offers a route to renewable fuel, but translating this reaction into systems suitable for industrial implementation remains difficult. Photocatalyst sheets can overcome key limitations of common direct water-splitting approaches (photoelectrochemical devices and photocatalyst dispersions), but existing photocatalyst sheets rely on inorganic semiconductor nanoparticles and processing techniques that can be difficult to scale. Here we show that solution-processed organic semiconductors can form water-splitting photocatalyst sheets by simply tailoring the charge extraction layer beneath the light-absorbing film. A single organic semiconductor active layer (deposited as a bulk heterojunction blend) drives either hydrogen or oxygen evolution depending on its underlying molecular contact, yielding photocathode and photoanode half-cells with well-matched photocurrents. Combining both reactions on one substrate using a microdomain-patterned molecular underlayer affords a photocatalyst sheet that achieves unassisted water splitting under simulated sunlight for over 2 h and generates hydrogen at a stabilized rate of 1.3 µmol h −1 cm −2 , which corresponds to a solar-to-hydrogen conversion efficiency of 0.1%.