Synergistic Crystallization and Surface Passivation: A Bifunctional Aminium Chloride Additive for High-Performance CsPbI ₂ Br Perovskite Solar Cells

Carbon-based all-inorganic perovskite solar cells (C-IPSCs) hold immense promise for low-cost, thermally robust photovoltaics, yet their efficiencies have been bottlenecked by poor film crystallinity and severe defect-induced nonradiative recombination. Here, we report a highly efficient two-step perovskite regulation strategy enabled by the bifunctional additive dimethylammonium chloride (DMACl), a capability uniquely absent in its mono- or trialkylammonium counterparts. DMACl initially forms a transient intermediate phase with the precursor, promoting compact, phase-pure α-CsPbI2Br films with significantly enlarged grains; upon annealing, it decomposes into volatile dimethylamine that volatilizes while concurrently passivating under-coordinated Pb2+ sites at surfaces and grain boundaries, enabling seamless transition from crystallization control to defect passivation and nearly eliminating nonradiative recombination. The resulting champion device delivers a PCE of 14.81% (versus 12.46% for the control), with negligible hysteresis and exceptional operational stability. By revealing the number of alkyl chains as a precise and powerful molecular design parameter, this strategy establishes a scalable, reproducible pathway to high-efficiency, ultrastable C-IPSCs suitable for commercialization.