Precursor-State Preorganization Narrows Crystallization Pathways in Formamidinium-Rich Perovskite Solar Cells

Formamidinium (FA)-rich perovskites in FA 1− x M x PbI 3 (M = MA and/or Cs) are promising photovoltaic absorbers, yet their crystallization proceeds through a congested landscape in which the photoactive α phase competes with nonphotoactive δ and polytype phases within a narrow thermodynamic window. As a result, the precursor diverges into multiple intermediate pathways. Here, we introduce (3-carboxypropyl)trimethylammonium chloride (CPTAC), a zwitterionic additive bearing a carboxylate head and a quaternary ammonium tail, which preorganizes the precursor via specific FA-CPTAC associations prior to nucleation. Two-dimensional 1 H nuclear magnetic resonance, together with in situ grazing-incidence wide-angle X-ray scattering, photoluminescence, and absorption measurements, reveals a contracted competing pathway, shortened intermediate lifetimes, and accelerated emergence of the α phase. This upstream pathway regulation translates into a denser and more homogeneous buried interface with reduced structural disorder. Inverted solar cells achieve power conversion efficiencies (PCEs) of 26.54% (0.1 cm 2 ) and 24.83% (1 cm 2 ). Unencapsulated devices retain 81% of their initial PCEs after 800 h at 85 °C, 97% after 1200 h under continuous illumination, and 98% after 1500 h under ISOS-D-1 storage conditions.