Point Defect Complexes in FAPbI3 and the Passivation with Modified Crown Ether Molecules

Exploring point defects in FAPbI3 and their passivation strategies is essential for optimizing the stability and optoelectronic properties of perovskite solar cells. In this work, the possible point defect complexes in FAPbI3 with PbI2-terminated and FAI-terminated structures have been explored using first-principles calculations. The results indicated that some point defect complexes were more stable than the corresponding individual point defects, including VFA + VPb + VI, PbFA + VPb, etc., in FAPbI3 with the PbI2-terminated structure, which induced obvious defect states within the band gap. Then, the defect passivation effect has been proposed and examined with a modified crown ether molecule (CE4-Cl) combined with the Li atom, which benefits from the natural atomic pore structure and prefers to bind with alkali metal atoms. The defect states induced by the point defect complex of VFA + VPb + VI were effectively eliminated, since the Cl ion successfully passivates the defect of VI and the Li atom offers additional electrons to passivate the defect of VFA. Moreover, the matched band alignment of type II enables the CE4-Cl molecule to serve as the passivation layer between FAPbI3 and the hole transport layer in perovskite solar cells. These results provide theoretical insights into the stability and the passivation strategy of the point defect complexes in FAPbI3, facilitating the performance improvement of perovskite-relevant optoelectronic devices.