Cl-based salts are magical additives to control the perovskite crystallization and enhance film morphology. Especially for the I/Br halide wide-bandgap (WBG) perovskites, alloying Cl to form triple halide perovskites can effectively enhance their optoelectronic characteristics. However, the alloying mechanism of Cl into the I/Br-based perovskite lattice remains unclear. Here, we conduct a systematic in-situ photoluminescence (PL) exploration on the crystallization processes of I/Br-based WBG with Cl-based additives including MACl and PbCl₂. The results reveal that only the Cl from PbCl₂ is easy to incorporate into the I/Br-based perovskite lattice structure at the initial stage of perovskite nucleation. However, PbCl₂ incorporation results in the precipitation of excess PbI₂, which leads to unfavorable charge transport and decreased photostability. With co-incorporation of MACl and CsCl, the transition of crystal orientation during the annealing process is effectively regulated, significantly eliminating the accumulation of excess PbI₂. This improvement enhances phase homogeneity and reduces defect density. Consequently, the optimized WBG perovskite solar cell achieves a high efficiency of 21.58%, which is the highest value for 1.68 eV perovskite with bromine content lower than 10%. In addition, the operational stability is significantly enhanced, along with ameliorated burn-in aging behavior.

All-inorganic perovskites are advantageous in terms of improved thermal stability compared to organic-inorganic counterparts. However, the ion migration-induced hysteresis significantly undermines the long-term operational stability of all-inorganic perovskite solar cells (PSCs), particularly in mixed halide perovskites. Herein, we report that tin-lead (Sn-Pb) alloying for all-inorganic mixed halide perovskites can effectively inhibit the ion migration behavior, as comprehensively revealed by the time-of-flight secondary ion mass spectrometry (TOF-SIMS), optical microscopy and galvanostatic measurements. On one hand, the small-sized Sn²⁺ cations can tighten the lattice structure to enhance the Pb/Sn-X (X=I and Br) ionic bonds, thereby effectively immobilizing the halide ions. On the other hand, Sn substitution can significantly reduce anti-site defects, such as I_Cs and I_Pb, which are considered potential pathways for ion migration. With these advantages, ion migration is greatly suppressed in Sn-Pb alloyed inorganic perovskites, resulting in reduced hysteresis and improved operational stability of PSC devices.