Dual‐Functional Molecular Stabilization of Spacer Cation‐Mediated Aging Dynamics in Low‐Dimensional Perovskite Precursors Enables Efficient Solar Cells

Abstract The aging dynamics of perovskite precursor solutions critically govern the photovoltaic performance of solar cells. However, the underlying degradation mechanisms in low‐dimensional perovskite precursors remain elusive, particularly regarding the pivotal role of spacer cations in modulating decomposition pathways. This study elucidates the intrinsic aging mechanisms in low‐dimensional perovskite precursors, revealing that spacer cation integration fundamentally governs decomposition kinetics. A dual‐functional solution stabilizer, 4‐carboxy‐2‐fluorophenylboronic acid (CFB), is strategically designed to concurrently mitigate precursor degradation and regulate crystallization dynamics. The carboxyl moiety undergoes spontaneous deprotonation to establish robust hydrogen bonds with guanidinium (GA + ), effectively suppressing methylamine (MA 0 )‐mediated nucleophilic attacks and preventing irreversible addition‐elimination reactions between GA + and MA 0 . Simultaneously, CFB orchestrates multi‐stage crystallization control through coordination modulation, yielding highly oriented perovskite crystals with passivated grain boundaries. The optimized devices demonstrate exceptional photovoltaic performance with a remarkably low energy loss of 0.38 eV. Notably, devices fabricated from aged precursors maintain 90% of initial efficiency over 42 days of ambient storage. Furthermore, unencapsulated devices deliver optimized humidity stability and thermal stability.