Chemical Functionality Engineering of Anti‐Solvent Additives for Photostable Perovskite Solar Cells

Metal-halide perovskite solar cells (PSCs) achieve high power-conversion efficiencies but remain susceptible to photo-induced degradation caused by mobile ions and phase segregation. Here, we investigate positional isomers of pyridine-carboxylic acid, namely pyridine-2-carboxylic acid (2-PC) and pyridine-4-carboxylic acid (4-PC), as anti-solvent additives to clarify how functional-group orientation governs defect passivation and photo-induced degradation. Both additives improve film morphology and reduce trap density; however, 4-PC, in which the carboxyl group is positioned opposite the pyridine nitrogen, provides markedly stronger passivation by virtue of its more favorable passivation geometry. As a result, 4-PC suppresses light-induced photoluminescence red shift, reduces trap density by approximately 27%, and enables unencapsulated devices to retain over 88% of their initial efficiency after 1000 h. Spectroscopic and transient analyses further indicate that 4-PC simultaneously passivates Pb-related defects and halide vacancies, thereby suppressing ion migration and halide phase segregation under operating conditions. These findings establish positional-isomer engineering as a practical molecular design principle for developing simple yet effective anti-solvent additives toward improved photo-induced phase stability in perovskite photovoltaics.