Highly Efficient and Stable Flexible Perovskite Solar Cells Enabled by Alkylammonium Acetate Modification with Varied Dipole Moments

Abstract Interface modification with the ability to passivate defects and regulate interface energy level is an important method to maximize the photovoltaic performance of perovskite solar cells (PSCs). Herein, through modifying the interface between perovskite and hole transport layer via different alkylammonium acetate ionic liquid molecules with varied dipole moments, efficient and stable PSCs are achieved. Especially, hexylammonium acetate (HAAc) with high dipole moment can reduce the energy difference between perovskite and hole transport layer to facilitate hole extraction and reduce energy loss. In addition, HAAc has a strong chemical binding ability to both acceptor and donor defects on perovskite surfaces through synergistic passivation of HA+ cation and Ac− anion, thereby reducing defect‐assisted recombination. The combined effects of energy level modulation and defect suppression lead to an overall enhancement in device performance. The best HAAc‐passivated device reaches an efficiency of up to 25.06% and maintains > 97.30% initial efficiency for 1000 h in air with 30 ± 10% humidity. In addition, the flexible perovskite solar cells exhibit excellent mechanical stability, with efficiency remaining above 71% of the initial value after 10 000 bending cycles at a small bending radius of 5 mm.