Protic Amine Carboxylic Acid Ionic Liquids Additives Regulate α‐FAPbI₃ Phase Transition for High Efficiency Perovskite Solar Cells

Abstract

Abstract The α‐phase formamidinium lead tri‐iodide (α‐FAPbI 3 ) has become the most promising photovoltaic absorber for perovskite solar cells (PSCs) due to its outstanding semiconductor properties and astonishing high efficiency. However, the incomplete crystallization and phase transition of α‐FAPbI 3 substantially undermine the performance and stability of PSCs. In this work, a series of the protic amine carboxylic acid ion liquids are introduced as the precursor additives to efficiently regulate the crystal growth and phase transition processes of α‐FAPbI 3 . The MA 2 Pb 3 I 8 ·2DMSO phase is inhibited in annealing process, which remarkably optimizes the phase transition process of α‐FAPbI 3 . It is noted that the functional groups of carboxyl and ammonium passivate the undercoordinated lead ions, halide vacancies, and organic vacancies, eliminating the deleterious nonradiative recombination. Consequently, the small‐area devices incorporated with 2% methylammonium butyrate (MAB) and 1.5% n‐butylammonium formate (BAFa) in perovskite show champion efficiencies of 25.10% and 24.52%, respectively. Furthermore, the large‐area modules (5 cm × 5 cm) achieve PCEs of 21.26% and 19.27% for MAB and BAFa additives, indicating the great potential for commercializing large‐area PSCs.