High-Photovoltage Perovskite–Organic Tandem Photovoltaics for Bias-Free Solar Ammonia Production

Efficient photovoltaic–electrochemical (PV–EC) systems for solar fuel production require photovoltaic devices that simultaneously provide high photovoltage, efficient charge extraction, and operational stability. Perovskite–organic tandem solar cells (PO-TSCs) are promising candidates owing to their high open-circuit voltage and compatibility with low-cost solution processing. In this work, we introduce a mixed hole-selective layer (m-HSL) formed by incorporating Al₂O₃ into a MeO-4PACz self-assembled monolayer through a simple one-step deposition process. The modified interface effectively suppresses interfacial losses and facilitates charge transport, enabling a PO-TSC with a power conversion efficiency of 22.85% and an open-circuit voltage of 2.13 V. Taking advantage of the high photovoltage, the tandem device is directly integrated with a two-electrode nitrate electrolyzer to achieve bias-free solar-driven nitrate reduction to ammonia. The integrated PV–EC system delivers a solar-to-ammonia efficiency of 3.7% together with a Faradaic efficiency of 82%. These results demonstrate the potential of interface-engineered PO-TSCs as efficient power sources for sustainable solar ammonia production and provide an effective strategy for bias-free nitrate electroreduction.