Bulk Heterojunction Organic Photoanodes for Enhanced Water Oxidation and Unassisted Solar Water Splitting

Polymer donors and non-fullerene acceptors have played an important role as photoactive materials in the development of high-efficiency organic solar cells, and they have immense potential for photoelectrochemical generation of solar fuels such as green hydrogen. However, their use in water-splitting photoelectrodes has been limited by their instability in aqueous environment and recombination losses at the interface with catalysts. Herein, PM6:D18:L8-BO organic photoanodes are presented reaching high photocurrent density over 25 mA cm-2 at +1.23 VRHE and unprecedented, days-long operational stability under solar illumination. This photoelectrochemical performance was achieved by protecting the photoactive layer by a graphite sheet functionalized with earth-abundant NiFeOOH water oxidation catalyst, providing both water resistance and electrical connection between the catalyst and the photoactive layer without any losses. This strategy also enables unassisted solar water splitting with solar-to-hydrogen efficiency of 5% by monolithic tandem organic photoanodes with PM6:D18:L8-BO and PTQ10:GS-ISO photoactive layers. These results pave the way towards high-efficiency, stable and unassisted hydrogen generation by low-cost organic photoelectrochemical cells.