Harnessing the Power of PM6:Y6 Semitransparent Photoanodes by Computational Balancement of Photon Absorption in Photoanode/Photovoltaic Organic Tandems: >7 mA cm⁻² Solar Synthetic Fuels Production at Bias-Free Potentials

This study first demonstrates the potential of organic photoabsorbing blends in overcoming a critical limitation of metal oxide photoanodes in tandem modules: insufficient photogenerated current. Various organic blends, including PTB7-Th:FOIC, PTB7-Th:O6T-4F, PM6:Y6, and PM6:FM, were systematically tested. When coupled with electron transport layer (ETL) contacts, these blends exhibit exceptional charge separation and extraction, with PM6:Y6 achieving saturation photocurrents up to 16.8 mA cm⁻² at 1.23 V_RHE (oxygen evolution thermodynamic potential). For the first time, a tandem structure utilizing organic photoanodes has been computationally designed and fabricated and the implementation of a double PM6:Y6 photoanode/photovoltaic structure resulted in photogenerated currents exceeding 7 mA cm⁻² at 0 V_RHE (hydrogen evolution thermodynamic potential) and anodic current onset potentials as low as −0.5 V_RHE. The herein-presented organic-based approach paves the way for further exploration of different blend combinations to target specific oxidative reactions by selecting precise donor/acceptor candidates among the multiple existing ones.