Buried-PV photocathodes were next assembled by coating the top Ag contact of the OPV devices with a conductive graphite epoxy (GE) paste. The device edges and wiring were further sealed with epoxy resin to prevent moisture infiltration and degradation (Supplementary Figs. ), and a 5 nm thin film of Pt was sputtered onto the dry GE layer as a H2 evolution catalyst. Cyclic voltammetry (CV) scans of the resulting photocathode (abbreviated OPV|GE|Pt) revealed an early onset potential of 1 V against the reversible hydrogen electrode (RHE), as well as a high photocurrent density of around -17 mA cm -2 at 0 V vs. RHE (Fig. ). These values stand out compared to previous reports, despite performing H2 evolution in a near-neutral, pH 8.5 solution as opposed to strongly acidic electrolytes (see Fig. and Supplementary Table for literature comparisons). The CV photocurrent was consistent with the -17.9±1.4 mA cm -2 value obtained from integrating the external quantum efficiency (EQE) spectrum at 0 V vs. RHE (Supplementary Fig. ). The EQE spectrum displayed a plateau between 550 and 700 nm, which mirrors the UV-vis spectrum (Supplementary Fig. ) and matches the reported EQE spectra of corresponding OPV cells, implying an effective charge generation and extraction across the OPV photocathode.