Regulation of Crystallization Kinetics via Zwitterionic Additive for Efficient and Operationally Stable Formamidinium Perovskite Solar Cells

Formamidinium (FA)‐based perovskite absorbers possess near‐ideal bandgaps for high‐performance solar cell applications; however, controlling their crystallization kinetics remains a critical bottleneck toward unlocking their full potential. Conventionally, methylammonium chloride (MACl) is introduced as a volatile crystallization additive to promote desired α‐phase formation despite severe drawbacks, including rapid nucleation, residual impurities, and associated defects. Here we introduce a zwitterionic additive, 2‐chloro‐1‐(3‐sulfopropyl)pyridinium (Cl‐PPS), that controls perovskite crystallization through cooperative coordination and hydrogen‐bonding interactions within the perovskite precursor solution. Cl‐PPS induces a uniform colloidal network that enables controlled nucleation, promotes direct α‐phase transformation, and passivates bulk and interfacial defects. The resulting films exhibit enhanced crystallinity, preferential vertical orientation, and a homogeneous potential landscape. Consequently, devices incorporating Cl‐PPS achieve a power conversion efficiency of 26.61%. Furthermore, the encapsulated devices retain 97.1% of their initial efficiency after 1200 h of continuous MPPT operation at 65°C in air.