Reducing Open-Circuit Voltage Losses in Wide-Bandgap FAPbBr₃ Perovskite Solar Cells for Continuous Unassisted Light-Driven Water Splitting

Wide-bandgap perovskite solar cells (PSCs) based on formamidinium lead bromide (FAPbBr₃) hold promise for unassisted solar-driven water splitting using a single-junction absorber. To meet the required thermodynamic voltage and overpotentials, nonradiative recombination in the PSC must be suppressed. Herein, a dual-passivation strategy is used that combines formamidinium thiocyanate (FASCN) for bulk passivation and 1,3-propane diammonium iodide (PDAI₂) for top surface passivation. FASCN promotes the growth of larger perovskite grains, while PDAI₂ mitigates surface defects, together leading to suppressed nonradiative recombination and improved charge extraction. Further optimization of the electron-transport layer (ETL) using a ternary fullerene blend (PCBM, CMC, ICBA) in a 1:1:1 weight ratio improves energetic alignment and suppresses interfacial energy losses, resulting in an increase in open-circuit voltage from 1.41 to 1.60 V and a power conversion efficiency of 9.4% in small-area devices. After scaling up to a 1.0 cm² active area, the PSC is integrated into a coupled photovoltaic-electrochemical (PV-EC) system for continuous solar-driven water splitting employing platinum (Pt) as the hydrogen evolution catalyst and ruthenium dioxide (RuO₂) as the oxygen evolution catalyst. The system achieves a solar-to-hydrogen (STH) efficiency of 6.5%, outperforming single-absorber PV-EC systems reported to date.