Unveiling\nthe Influence of Additive Acidity on the\nLong-Term Stability of Perovskite Solar Cells

Additive engineering plays a vital role in enhancing\nperovskite\nsolar cells (PSCs) by passivating defects within the perovskite films.\nCarboxyl and ester groups are commonly used for their strong binding\nwith under-coordinated Pb<sup>2+</sup> ions. However, the impact of\nadditive acidity on the long-term stability of PSCs remains unclear.\nThis study investigates the functional roles of 4-amino-3,5-difluorobenzoic\nacid (DFAB-A) and methyl 4-amino-3,5-difluorobenzoate (DFAB-AM), which\ncould effectively passivate the film defects. However, the acidity\nresulting from carboxyl deprotonation in DFAB-A negatively impacts\nthe structural stability of the perovskites. In contrast, DFAB-AM\nwith its ester functionality forms stronger and more stable bonds,\ncontributing to improved passivation and stability. PSCs incorporating\nDFAB-AM achieve a high power conversion efficiency of 22.51% and maintain\n84.3% of their initial efficiency after 800 h of maximum-power-point\noperation. These findings underscore the importance of carbonyl group\ndesign in developing molecular additives to enhance both the efficiency\nand the durability of PSCs.