Organic Semiconductor-BiVO₄ Tandems for Solar-Driven H₂O and CO₂ Splitting

Photoelectrochemical (PEC) devices offer great promise for simultaneous solar light harvesting and chemical storage, converting water and CO₂ into value-added products.¹ While progress has been made to improve their solar-to-fuel conversion efficiencies, most conventional inorganic prototypes face challenges in terms of insufficient photovoltage, moisture instability, high material cost or toxicity.^2-5 In this work, we introduce PEC devices based on an organic π-conjugated donor-acceptor bulk heterojunction, protected by a carbon-based encapsulant to produce green H₂ and the platform chemical CO. By rationally combining design strategies from both organic photovoltaic and PEC fields, the photocathodes achieve long-term H₂ production over 300 h, which is tenfold higher than reported systems. Further interfacing the devices with a molecular CO₂ reduction catalyst allow for tunable and selective CO production under 0.1 sun. The complementary light absorption of these photocathodes with BiVO₄ enable their assembly into a standalone artificial leaf, demonstrating unassisted concurrent CO₂ reduction and water oxidation over 96 h. This establishes a new path for organic semiconductors, as we approach the composition, function, and efficiency of natural leaves.<br/><br/><b>References:</b><br/>1. Tuller, H. L. Solar to fuels conversion technologies: a perspective. <i>Materials for Renewable and Sustainable Energy</i> <b>6</b>, 3 (2017).<br/>2. Lin, Y.<i> et al.</i> Amorphous Si Thin Film Based Photocathodes with High Photovoltage for Efficient Hydrogen Production. <i>Nano Letters</i> <b>13</b>, 5615-5618 (2013).<br/>3. Goto, Y.<i> et al.</i> A particulate (ZnSe)_0.85(CuIn_0.7Ga_0.3Se₂)_0.15 photocathode modified with CdS and ZnS for sunlight-driven overall water splitting. <i>Journal of Materials Chemistry A</i> <b>5</b>, 21242-21248 (2017).<br/>4. Pan, L.<i> et al.</i> Boosting the performance of Cu₂O photocathodes for unassisted solar water splitting devices. <i>Nature Catalysis</i> <b>1</b>, 412-420 (2018).<br/>5. Andrei, V.<i> et al.</i> Scalable Triple Cation Mixed Halide Perovskite-BiVO₄ Tandems for Bias-Free Water Splitting. <i>Advanced Energy Materials</i> <b>8</b> (2018).