Inorganic‐Organic Synergistic Passivation via Grain Boundary‐Selective ALD‐Al ₂ O ₃ and Piperazine‐1,4‐diium Iodide for Efficient Wide‐Bandgap Perovskite Solar Cells

ABSTRACT The perovskite top interface remains a primary source of non‐radiative recombination and environmental degradation in inverted perovskite solar cells (PSCs). While atomic layer deposition (ALD) of Al ₂ O ₃ offers potential for interface passivation, its reactive precursors often induce parasitic decomposition of the underlying perovskite. Herein, we report a synergistic inorganic–organic passivation strategy that integrates site‑selective ALD‑Al ₂ O ₃ with full‑surface piperazine‐1,4‐diium iodide (PDI) treatment. Under controlled low‐cycle ALD, Al ₂ O ₃ preferentially nucleates as discrete islands rather than a continuous film, selectively anchoring at perovskite grain boundaries while simultaneously promoting grain growth. By optimizing the precursor pulse time, we achieve effective grain boundary decoration with minimal perovskite decomposition. This spatially targeted inorganic passivation is then complemented by PDI, which heals residual defects across the entire perovskite surface. The resulting inorganic–organic dual‑passivation scheme delivers a “1 + 1>2” enhancement. Consequently, wide‑bandgap (1.67 eV) inverted PSCs incorporating this strategy achieve a champion power conversion efficiency of 22.38% with a high open‑circuit voltage of 1.26 V, and markedly improved storage and moisture stability. This work establishes a new paradigm for interface engineering by harnessing the unique nucleation behavior of ALD‐grown oxides for synergistic passivation in high‐performance perovskite photovoltaics.