Enhanced Defect Passivation and Crystallization Control via Carboxyl‐Functionalized Additive in Inverted Perovskite Solar Cells Delivering 26.53% Efficiency and Superior Stability

In this study, an additional carboxyl (─COOH) group was introduced into a molecular framework containing cyano (─C≡N) and amino (─NH 2 ) functionalities to construct the multifunctional additive 4‐ACBA, with 3‐ABN employed as a structurally related reference. This molecular comparison was designed to investigate how the introduction of the additional carboxyl functionality affects molecular‐perovskite interactions, film crystallization, and defect‐related processes. Comparative NMR measurements and DFT calculations support stronger interactions between 4‐ACBA and Pb‐related species than those of 3‐ABN, while XPS reveals corresponding changes in the local chemical and electronic environment of the perovskite surface. Structural characterization further shows that 4‐ACBA regulates perovskite crystallization and phase evolution, accompanied by substantially suppressed secondary‐phase signatures. Meanwhile, enhanced photoluminescence and prolonged carrier lifetime indicate suppressed defect‐mediated nonradiative recombination. Benefiting from these combined effects, the 4‐ACBA‐modified device achieves a champion power conversion efficiency of 26.53%, outperforming the 3‐ABN‐based device (26.01%) and the control device (24.69%). Moreover, the encapsulated 4‐ACBA device retains 86.38% of its initial efficiency after 1200 h of dark storage at 65°C and 85% RH. These results demonstrate that multifunctional molecular integration provides an effective strategy for simultaneously regulating perovskite film formation and defect‐related processes in high‐performance inverted perovskite solar cells.