Surface Engineering for Enhanced Perovskite Solar Cells: Fullerene-Mediated Trap State Formation on CsPbI3 (001) Surface

Photovoltaic technology, particularly perovskite solar cell (PSC) materials, has emerged as a promising avenue due to their excellent light-absorbing properties. Despite significant progress in PSC technology, defects within the perovskite material continue to pose challenges, leading to reduced efficiency and stability of the devices. CsPbI3 perovskites have shown potential, but trap states induced by surface defects remain a challenge. The use of fullerene-derivatives, like C60 and PC61BM, has been highlighted to enhance the device stability eliminating/reducing hysteresis and passivating trap states. However, the mechanisms behind fullerene-induced passivation of trap states and their impact on surface energetics remain unclear. This study employs periodic density functional theory (DFT) simulations to explore the interaction between C60, PC61BM, and CsPbI3 (001) surface, with and without defects (cesium vacancy, lead vacancy, and I-antisite). The DFT simulations reveal that both C60 and PC61BM effectively passivate trap states induced by I-antisite defects by reorienting and reorganizing the iodine atoms that promote the presence of trap states. This work contributes to understanding the fundamental aspects of surface-defect interactions in CsPbI3 perovskites. Both C60 and PC61BM play a crucial role in passivating trap states, causing atomic reorganization and avoiding the nonradiative recombination. The findings provide valuable insights into mechanisms for trap state passivation by fullerene derivatives, paving the way for further research to enhance PSC performance.