Stage‐Resolved Synergy of Tri‐Functional Additive in Perovskite Crystallization for High‐Efficiency Wide‐Bandgap Perovskite and Tandem Solar Cells

Uncontrolled crystallization from the precursor solution to nucleation and final film formation—leads to high defect density and phase segregation, which limit both the efficiency and stability of wide‐bandgap (WBG) perovskite/silicon tandem solar cells. However, most existing additives are constrained by their molecular structure, acting only at limited formation stages and lacking stage‐resolved mechanistic understanding. As a result, they offer insufficient control over nucleation kinetics and defect passivation. Here, an additive with three distinct functions—potassium dimethylaminomethyl trifluoroborate (PDT)—in which the BF 3 − group coordinates with Pb 2 ⁺ to regulate the precursor environment, promotes an ordered intermediate phase to delay crystallization is designed, and the dimethylamino group passivates buried interfaces and grain boundaries to suppress ion migration. Unlike conventional additives that act at a single stage, our strategy enables regulation of nucleation, crystal growth, and interface passivation across the entire formation process. Ultimately, PDT‐modified WBG perovskite cells reach a PCE of 22.56% with improved stability, while the unencapsulated perovskite/silicon tandem devices deliver a 32.33% PCE (certified 31.93%) and a V oc of 1.94 V, retaining 85% of its initial efficiency after 788 h of continuous operation.