Accelerated Formation of CsPbI ₃ through Controlled Amidation of Intermediate Phases

The all‐inorganic metal halide perovskite CsPbI 3 is a promising photovoltaic absorber owing to its thermal stability and suitable bandgap for tandem applications. The most common approach to depositing CsPbI 3 from solution is based on the use of dimethylammonium iodide (DMAI); however, removing DMAI during crystallization is challenging, as it introduces residues that can lead to higher defect densities and trigger degradation. Here, we introduce a reaction‐guided crystallization strategy based on 2,2,2‐trifluoroethyl trifluoroacetate (TFTF), which undergoes a rapid ester‐amine amidation reaction with DMAI during annealing. By converting DMAI into highly volatile products, the TFTF reaction drives a smooth, additive residue‐free transition to γ‐CsPbI 3 and produces pinhole‐free films with low defect densities. Devices fabricated using this strategy deliver an open‐circuit voltage (V OC ) of 1.20 V and a champion efficiency of 20.8%, along with markedly improved operational stability. This intermediate‐management approach provides a practical, chemically defined pathway for directing CsPbI 3 crystallization and advancing high‐performance inorganic iodide perovskite photovoltaics.