Modulating Molecular Interaction of Benzimidazole Derivatives Via Isomerization Toward Rational Additive Engineering for Printable Mesoscopic Perovskite Solar Cells

Defect states at the boundaries and the perovskite/electron transport layer (ETL) interface critically induce charge recombination in printable mesoscopic perovskite solar cells (p‐MPSCs). Herein, we engineer the defect management by introducing two multifunctional benzimidazole derivative additives, 1H‐benzimidazole‐2‐carboxylicacid (2‐CBIm) and 5‐benzimidazolecarboxylic acid (5‐CBIm), which are isomers with different functional group positions, for improving the performance of p‐MPSCs. The functional group position differences modulate the defect passivation ability of 2‐CBIm and 5‐CBIm in p‐MPSCs. 5‐CBIm, featuring desired distribution of the carboxyl group and the imidazole group, presents superior binding with perovskite and the TiO 2 ETL than 2‐CBIm, whose interaction ability is influenced by the steric effect. The enhanced interaction facilitates defect passivation and nonradiative recombination suppression in p‐MPSCs. Consequently, the 5‐CBIm device achieves a well‐improved champion power conversion efficiency (PCE) of 20.61%, surpassing the 2‐CBIm device (19.40%) and the control device (18.17%). This work contributes to a better understanding of structure–property relationships and opens extended possibilities for designing advanced defect passivation additives.