Maximizing Defect Formation Energies via Collaborative Passivation Achieves High-Performance Perovskite Solar Cells

Artless external interference cannot completely eliminate the intrinsic defects stemming from the soft ionic nature of the perovskite. Therefore, improving the defect formation energies to evade the defects at the root has become an internal driving force for attaining high-performance perovskite solar cells (PSCs). We hereby report that a new additive molecule, namely, cesium(I) bis(trifluoromethanesulfonyl)imide (CBTI), can effectively handle the intricate intrinsic defects present in the perovskite film. More specifically, the S═O groups within CBTI can chemically anchor uncoordinated Pb²⁺ at grain boundaries and surfaces, while the -CF₃ groups can immobilize organic cations via hydrogen bonding, which are beneficial for reinforcing the perovskite lattice and consequently improving the formation energy of each defect, namely, iodine vacancy (V_I), lead vacancy (V_Pb), Pb-I antisite (I_Pb), and I-Pb antisite (Pb_I). Consequently, the optimized PSCs deliver a power conversion efficiency of 24.42% and exhibit excellent stability, retaining 90.8% of their initial performance after 1200 h in ambient air and 80.6% following 500 h of continuous illumination.