Unveiling the Influence of Additive Acidity on the Long-Term Stability of Perovskite Solar Cells

Additive engineering plays a vital role in enhancing perovskite solar cells (PSCs) by passivating defects within the perovskite films. Carboxyl and ester groups are commonly used for their strong binding with under-coordinated Pb 2+ ions. However, the impact of additive acidity on the long-term stability of PSCs remains unclear. This study investigates the functional roles of 4-amino-3,5-difluorobenzoic acid (DFAB-A) and methyl 4-amino-3,5-difluorobenzoate (DFAB-AM), which could effectively passivate the film defects. However, the acidity resulting from carboxyl deprotonation in DFAB-A negatively impacts the structural stability of the perovskites. In contrast, DFAB-AM with its ester functionality forms stronger and more stable bonds, contributing to improved passivation and stability. PSCs incorporating DFAB-AM achieve a high power conversion efficiency of 22.51% and maintain 84.3% of their initial efficiency after 800 h of maximum-power-point operation. These findings underscore the importance of carbonyl group design in developing molecular additives to enhance both the efficiency and the durability of PSCs.