Unifying the Colloidal Homogeneity of Perovskite Precursor for Perovskite Solar Cells

Recent advances in solution-processed metal halide perovskites recognize precursor solutions as complex colloidal suspensions where additive engineering critically influences crystallization kinetics and film morphology. While additives have been widely reported to suppress trap defects, their roles in regulating the colloidal coordination environment, particularly the bimodal size distribution of the perovskite solution, remain elusive. Here, we demonstrate trifluoroacetic acid (TFA) as a single-molecule multifunctional agent that uniquely reconfigures colloidal suspensions of a perovskite precursor. TFA's strong electron-withdrawing effect protonates the solvent molecules, shifting solution pH from alkaline to acidic and collapsing bimodal distributions into homogeneous small colloids via dissolution of iodoplumbate aggregates ([PbI_mX_n]^2-). Concurrently, TFA enhances homogeneous nucleation through direct precursor coordination and unifies crystal growth. This dual control yields films with reduced defects and improved crystallinity, achieving a PCE increase from 23.3% to 25.2% with synergistic gains in V_OC, J_SC, and FF. Our work emphasizes the crucial roles of unifying the colloidal homogeneity of the perovskite precursor solution in advancing the perovskite solar cell performance.