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

All-inorganic cesium-lead-iodide (CsPbI 3 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 (CsPbTh 3 ) solar cells. Both theoretical simulations and experimental measurements reveal that the noncoordinating anions, PF 6 - , as a Lewis base can more effectively bind with undercoordinated Pb 2+ to passivate iodide vacancy defects than the BF 4 - and absorbed I - , and thus the point defects are well suppressed. In addition, N-propyl-methyl piperidinium (NPMP + ) is selected to assemble with PF 6 - in CsPbTh 3 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 CsPbTh 3 solar cells to 19.02% under 1-sun illumination (100 mW cm -2 ). Fortunately, the NPMP + and PF 6 - -treated CsPbTh 3 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.