Although acidic, hygroscopic PEDOT:PSS hole selective layers are known to promote device degradation in aqueous solutions, the GE enabled an effective moisture encapsulation. Accordingly, an OPV|GE|Pt photocathode could demonstrate long-term H2 evolution over 300 h of chronoamperometry (CA) at 0 V vs. RHE, producing 27.0 mmol cm -2 H2 with faradaic yields (FY) of ~90% (Fig. ). This stability was reproducible over 48 h, with three photocathodes attaining 7.15±0.40 mmol cm -2 of H2 (80.9±7.3% FY) over 48 h CA at 0 V vs. RHE (Supplementary Fig. ). The decay in photocurrent density with time was partially recovered by replacing and re-purging the buffer solution every 48 h (Fig. ). However, this trend was sustained even after Pt re-deposition at 240 h, which indicates that stability is primarily governed by the buried PV device degradation. This was supported by CV scans after 48 h and 300 h of CA, which revealed a progressive decrease in both onset potential and photocurrent (Supplementary Fig. ). This gradually decreasing trend is analogous to the initial photoinduced burn-in and long-term linear decay regimes characteristic of OPVs, which may be due to UV-light exposure from the solar simulator and interfacial degradation. Nano-cracks also appeared across the Pt surface after the long-term CA test (Supplementary Fig. ), as observed in previous reports.