Suppressing Deprotonation to Extend the Shelf Life of Perovskite Precursor Solutions and Enhance the Stability and Efficiency of Perovskite Solar Cells

Abstract Amid the rapid advancement of formamidine (FA)‐based perovskite solar cells (PSCs), methylammonium chloride (MACl) has emerged as a pivotal molecule, widely recognized in achieving high‐efficiency PSCs. However, in perovskite precursor solution (PPS), particularly after prolonged storage, deprotonated MA⁺ (MA⁰) undergoes cationic addition with FA⁺, leading to a relative depletion of FA⁺ and a reduction in crystalline phase purity. Herein, using Piperazine‐2‐carboxylic acid dihydrochloride (PCADCl) to inhibit MA⁺ deprotonation by forming strong two‐point hydrogen bonds between the piperazine's amine groups and proton (H⁺) of MA⁺is proposed, thereby extending the shelf life of the PPS. Furthermore, COOH groups of PCADCl furtherly suppress MA⁺ deprotonation while promoting coordination with unbound Pb²⁺, reducing film defects and improving the purity of the perovskite crystalline phase. Additionally, the energy level arrangement of the PSCs is improved. Benefiting from this strategy, the PSC fabricated with the modified PPS achieves an impressive efficiency of 25.56% and retains 96% of its initial performance after solution aging for 20 days. Moreover, the unencapsulated device retains 97% of its initial efficiency over 1300 h. This work significantly advances process development and scientific research, representing a crucial step toward the large‐scale production and commercialization of PSCs.