Integrating low-cost earth-abundant co-catalysts with encapsulated perovskite solar cells for efficient and stable overall solar water splitting

Metal halide perovskite solar cells have an appropriate bandgap (1.5–1.6 eV), and thus output voltage (>1 V), to directly drive solar water splitting. Despite significant progress, their moisture sensitivity still hampers their application for integrated monolithic devices. Furthermore, the prevalence of the use of noble metals as co-catalysts for existing perovskite-based devices undermines their use for low-cost H₂ production. Here, a monolithic architecture for stable perovskite-based devices with earth-abundant co-catalysts is reported, demonstrating an unassisted overall solar-to-hydrogen efficiency of 8.54%. The device layout consists of two monolithically encapsulated perovskite (FA_0.80MA_0.15Cs_0.05PbI_2.55Br_0.45) solar cells with low-cost earth-abundant CoP and FeNi(OH)_x co-catalysts as the photocathode and photoanode, respectively. The CoP-based photocathode demonstrates more than 17 h of continuous operation, with a photocurrent density of 12.4 mA cm⁻² at 0 V and an onset potential as positive as ≈1 V versus reversible hydrogen electrode (RHE). The FeNi(OH)_x-based photoanode achieves a photocurrent of 11 mA cm⁻² at 1.23 V versus RHE for more than 13 h continuous operation. These excellent stability and performance demonstrate the potential for monolithic integration of perovskite solar cells and low-cost earth-abundant co-catalysts for efficient direct solar H₂ production.