A Dual Functional Polymer Interlayer Enables Near‐Infrared Absorbing Organic Photoanodes for Solar Water Oxidation

Organic photovoltaic devices employing bulk heterojunctions (BHJs) of polymer donors and small molecular nonfullerene acceptors have recently demonstrated high performance, with strong visible and near-infrared absorption and low energy losses. Such junctions are promising candidates for solar-driven water splitting; however, the poor underwater stability of the small molecular acceptor in such devices has limited their viability to date. Here, a stable and efficient organic photoanode is demonstrated for water oxidation based upon a Y6:PM6 BHJ with a further dual functional PM6 layer transferred from water, and Au/NiFe electrocatalyst top layers. The additional PM6 layer functions to 1) increase operational stability and 2) suppress recombination losses between the BHJ and electrocatalyst layers. These BHJ/PM6 based photoanodes exhibit a photocurrent density of 4.0 mA cm(-2) at 1.23 V versus the reversible hydrogen electrode and promising operational stability compared to the anode without a PM6 layer, maintaining a photocurrent >= 2 mA cm(-2) over 1 h. Employing these photoanodes, solar water oxidation under near-infrared irradiation is demonstrated with an incident photon-to-current efficiency up to 25% at 770 nm illumination.