Dual-timescale crystallization engineering enabling direct α-FAPbI3 formation for high-efficiency antisolvent-free perovskite solar cells

FAPbI3 has been extensively employed in high-performance perovskite solar cells (PSCs) owing to its optimal bandgap and outstanding optoelectronic properties. Nevertheless, it readily undergoes the formation of a photo-inactive δ-phase during crystallization, and achieving high-quality α-phase films becomes even more challenging in antisolvent-free fabrication processes. This study introduces a crystallization control strategy based on 2-dimethylaminopyridine (2-DMAP) ligand engineering to establish a “fast nucleation-slow growth” dual-time-domain crystallization mechanism. 2-DMAP facilitates the formation of a functional intermediate phase (2-DMAP·PbI2·DMSO) that enables a direct transformation to the α-FAPbI3 phase and effectively suppresses the δ-phase pathway. Theoretical calculations and systematic experimental characterizations demonstrate that 2-DMAP exhibits stronger binding affinity and a greater charge polarization effect than dimethylsulfoxide (DMSO). This promotes the formation of high-density nuclei during spin coating and delays excessive grain growth during annealing, leading to perovskite films with improved crystallinity, fewer defects, and longer carrier lifetimes. As a result, an antisolvent-free PSC device was successfully fabricated, achieving a power conversion efficiency (PCE) of 25.10 %, one of the highest reported for antisolvent-free spin-coating systems. Under ISOS-L-1 standard conditions, the device retained 84.78 % of its initial efficiency after 1500 h of continuous illumination, demonstrating excellent operational stability. Moreover, it exhibited remarkable long-term stability under harsh humid and thermal conditions. This work offers a valuable strategy for the large-scale fabrication of high-performance and antisolvent-free PSCs.