A Polymer Overlayer Generates Long-Lived Charges in PM6:Y6 Bulk-Heterojunction Photoanodes with Improved Photoelectrocatalytic Performance

Photogenerating charges with long lifetimes to drive catalysis is challenging in organic semiconductors. Here, we investigate the role of a PM6 polymer overlayer on the photoexcited carrier dynamics in a PM6:Y6 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. We demonstrate 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% was observed using 850 nm excitation. We propose 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.