Designing organic semiconductor-BiVO 4 tandem devices for H 2 O and CO 2 splitting Celine Wing See Yeung 1 , Virgil Andrei 1,2 , Tack Ho Lee 3,† , James Robert Durrant 3 , Erwin Reisner 1,* 1 Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom, 2 Optoelectronics Group, Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom, 3 Department of Chemistry and Centre for Processable Electronics, Imperial College London, London W12 0BZ, United Kingdom, † Present address: Department of Chemistry Education, Graduate Department of Chemical Materials, Institute for Plastic Information and Energy Materials, Sustainable Utilization of Photovoltaic Energy Research Center, Pusan National University, Busan 46241, Republic of Korea * reisner@ch.cam.ac.uk Photoelectrochemical (PEC) devices mimic photosynthesis by integrating light absorbers with suitable catalysts to directly harness, convert, and store abundant solar energy in the form of value-added chemical fuels. [1] However, most conventional prototypes employ wide bandgap semiconductors, moisture-sensitive inorganic light absorbers, expensive materials or corrosive electrolytes. This presentation will start from the rational design of organic photovoltaic (OPV) layers, followed by the assembly of PEC devices that contain the donor-acceptor bulk heterojunction (PCE10:EH-IDTBR). Sufficient photovoltage is generated for both proton reduction and CO 2 - to-syngas conversion in benign aqueous media, thereby tackling the main bottleneck in the organic PEC field and proving that acidic buffers are not always needed for optimal performance. [2] Protection by a carbon-based encapsulant promoted long-term H 2 production with platinum over 12 days, while interfacing the devices with a molecular cobalt porphyrin catalyst allowed for tunable and selective CO production under 0.1 sun. Their early onset potentials and complementary light absorption with BiVO 4 enable the assembly of PCE10:EH-IDTBR – BiVO 4 standalone artificial leaves, operating over 96 h completely powered by sunlight. This establishes a new path for organic semiconductors, as we approach the composition, function, and efficiency of natural leaves. References 1. H. L. Tuller, Mater. Renew. Sustain. Energy 2017 , 6 , 3. 2. C. W. S. Yeung, V. Andrei, T. H. Lee, J. R. Durrant, E. Reisner, Adv. Mater. 2024 , 2404110.
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