Long‐Lived Charges in Y6:PM6 Bulk‐Heterojunction Photoanodes with a Polymer Overlayer Improve Photoelectrocatalytic Performance

Abstract Photogenerating charges with long lifetimes to drive catalysis is challenging in organic semiconductors. Here, the role of a PM6 polymer overlayer on the photoexcited carrier dynamics is investigated in a Y6:PM6 bulk‐heterojunction (BHJ) photoanode undergoing ascorbic acid oxidation. With the additional polymer layer, the hole lifetime is increased in the solid state BHJ film. When the photoanode is electrically coupled to a hydrogen‐evolving platinum cathode, remarkably long‐lived hole polaron states are observed on the timescale of seconds under operational conditions. It is demonstrated that these long‐lived holes enable the organic photoanode with the polymer overlayer to show enhanced ascorbic acid oxidation performance, reaching ≈7 mA cm −2 at 1.23 V RHE without a co‐catalyst. An external quantum efficiency of 18% is observed using 850 nm excitation. It is proposed that the use of an organic overlayer can be an effective design strategy for generating longer charge carrier lifetimes in organic photoanodes for efficient oxidation catalysis.