Revealing Defect Passivation and Charge Extraction by Ultrafast Spectroscopy in Perovskite Solar Cells through a Multifunctional Lewis Base Additive Approach

Defect passivation inside the crystal lattice and the grain-boundary (GB) surface of the perovskite films has become the most effective strategy to suppress the negative impact of the nonradiative recombination in perovskite solar cell. In this study, a unique approach to effectively passivate the defect states of MAPbI(3) perovskite thin film using thionicotinamide (TNM) as a multifunctional Lewis base additive is demonstrated. TNM as an additive with three different types of Lewis base sites, i.e., pyridine, amino, and C=S functional groups, is introduced to mitigate the trap states in the TNM-modified perovskite films and thoroughly investigate the passivation defects. The nonbonded electron of the three different Lewis base sites can synergistically passivate the antisite lead (Pb) defects and improve the stability of the device. In addition, the -NH2 group can form ionic bonds with negatively charged I- ions and inhibit ion migration caused by them. It is found that such passivation effect of TNM reduces the GB defects and improves the crystallinity significantly. As a result, a champion TNM-modified device shows an improved power conversion efficiency of 19.26% from 16.86% along with enhanced open-circuit voltage, fill factor, and negligible hysteresis.