π-π stacking arrangement of naphthoic acid enhanced bulk passivation for efficient perovskite solar cells

Lewis base molecules have been extensively employed for defect passivation in perovskite solar cells (PSCs) due to their ability to effectively coordinate with undercoordinated lead ions and enhance device performance. However, current research predominantly focuses on the influence of molecular configurations, while largely neglecting the critical role of molecular arrangements in determining passivation efficiency. In this work, to systematically investigate the defect passivation mechanism governed by molecular arrangements of Lewis base molecules, we designed three carboxylic acid (-COOH) functionalized ligands featuring non-conjugated (cyclohexanecarboxylic acid) and conjugated (1-naphthoic acid and 2-naphthoic acid) structures as passivating agents. Compared to the non-conjugated ligand, the conjugated naphthalene core establishes conjugation interactions with the perovskite surface, inducing a preferential lying-down orientation. More importantly, the intermolecular π-π stacking of conjugated functional groups extends π-electron delocalization, thereby providing sufficient electron density to fill defect states. As designed, the conjugated ligands demonstrate superior capability in passivating undercoordinated Pb^{2 +} ion defects and immobilizing iodide anions. This π-π stacking strategy significantly enhances the power conversion efficiency of PSCs from 24.07 % to 25.76 %, offering an effective molecular design approach for optimizing the performance of PSCs through rational control of Lewis base stacking arrangements.