Abstract
The optimal selection of alkyl chains and halogen ions in ammonium salts for addressing specific defect types in perovskite films remains unclear, although ammonium salts emerged as a promising strategy to enhance the performance of perovskite solar cells (PSCs). Herein, four ammonium salts are introduced with different alkyl chain types and halogen ions to passivate perovskite films. Branched-alkyl chain ammonium salts exhibited superior passivation effects compared to linear-alkyl chain salts, with the alkyl chain structure having a more significant impact on device performance than the halogen ion component. In addition, DFT calculations are performed to investigate which defect types in perovskite films are most effectively passivated by different alkyl chain types and halogen ions in ammonium salts. Branched-alkyl chain ammonium salts demonstrated superior passivation effects on VPb and VFA defects in perovskite films compared to linear-alkyl chain salts, while exhibiting similar passivation effects for VI defects. PSCs passivated with tert-OAI achieved an impressive efficiency of 25.49%, with a Voc of 1.19 V, a Jsc of 25.40 mA cm- 2, and an FF of 84.34%. This work highlights a targeted ammonium salt passivation strategy tailored to address different defect types in perovskite films, accounting for variations in perovskite composition and fabrication environments.