Integrating Low‐Cost Earth‐Abundant Co‐Catalysts with Encapsulated Perovskite Solar Cells for Efficient and Stable Overall Solar Water Splitting

Abstract 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 H 2 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 0.80 MA 0.15 Cs 0.05 PbI 2.55 Br 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 H 2 production.