Lewis Acid-Base Adducts for Efficient and Stable Cesium-Based Lead Iodide-Rich Perovskite Solar Cells

All-inorganic cesium-lead-iodide (CsPbI₃ Br_{3- x} (2 < x < 3)) perovskite presents preeminent photovoltaic performance and chemical stability. Unfortunately, this kind of material suffers from phase transition to a nonperovskite phase under oxidative chemical stresses. Herein, the introduction of a low concentration of Lewis acid-base adducts (LABAs) is reported to synergistically reduce defect density, optimize interfacial energy alignment, and improve device stability of CsPbI_2.75 Br_0.24 Cl_0.01 (CsPbTh₃ ) solar cells. Both theoretical simulations and experimental measurements reveal that the noncoordinating anions, PF₆ ^- , as a Lewis base can more effectively bind with undercoordinated Pb²⁺ to passivate iodide vacancy defects than the BF₄ ^- and absorbed I^- , and thus the point defects are well suppressed. In addition, N-propyl-methyl piperidinium (NPMP⁺ ) is selected to assemble with PF₆ ^- in CsPbTh₃ film. The NPMP⁺ can regulate the crystal growth and finally homogenize the grain size and decrease the trap density. Consequently, the LABAs strategy can improve the power conversion efficiency of CsPbTh₃ solar cells to 19.02% under 1-sun illumination (100 mW cm^-2 ). Fortunately, the NPMP⁺ and PF₆ ^- -treated CsPbTh₃ film shows great phase stability after storage in ambient air for 250 days, and the power conversion efficiency of corresponding solar cells is almost 76% of the initial value after 60 days aging under ambient conditions.