Stepwise multi-target optimization of two-step deposition for wide-bandgap perovskite solar cells

The two-step deposition for fabricating wide-bandgap (WBG) perovskite solar cells (PSCs) offers superior controllability and reproducibility over the conventional one-step antisolvent method. Nevertheless, achieving high-quality films remains challenging because the first-step PbI₂ template directly governs mass transport and reaction kinetics in the second step, leading to strong interdependence between processing parameters. Conventional single-step or individual additive-focused optimizations fail to address these coupled effects, limiting systematic improvements in film quality. Here, we implement a stepwise, multi-target optimization strategy to systematically refine six critical processing variables and simultaneously optimize multiple performance-related objectives, including tandem-compatible bandgap and photostability. Under the optimized conditions, the resulting films (1.73 eV) exhibit enlarged grain sizes, reduced defect densities, and improved photostability. Devices fabricated from these optimized films achieve a power conversion efficiency (PCE) of 17.61%, significantly exceeding the 15.15% of control devices. This work establishes a robust, data-driven pathway for advancing two-step deposition toward high-performance, tandem-compatible WBG PSCs.