Passivation effect of potassium cation-18-crownether-6 on FAPbI3(001) perovskite surface: a first-principles study

Passivation treatment is an important way to reduce the defect density of perovskites, which has been proven to be highly effective in improving the long-term stability and high performance of perovskite solar cells (PSCs). In this work, the passivation effects of potassium cation-18-crownether-6 (18C6–K⁺) molecules on the surface defects of FAPbI₃(001) were investigated by using first-principles calculations. The adsorption energy of 18C6–K⁺ small molecule on the defective surface were calculated to be negative, indicating stable adsorption on the FAPbI₃(001) surface. Calculations of defect energy levels showed that V_I and I_i defects are shallow-level defects, while I_Pb, Pb_I, and Pb_i defects are deep-level defects. And V_Pb acts as a deep-level defect on the PbI₂-terminated surface, while as a shallow-level defect on the FAI-terminated surface. After 18C6–K⁺ passivation, the defect formation energies of vacancy (V_I), interstitial (Pb_i), and antisite (Pb_I) increased, suggesting inhibition of defects formation on the FAPbI₃(001) surface. Work function analysis reveals that the introduction of 18C6–K⁺ molecules facilitates electron transitions by reducing the work function and enhancing the alignment of energy levels. The TDOS analysis, combined with CDD calculations, indicates that the passivation mechanism by 18C6–K+ is predominantly due to interactions between iodine (I) and ether (C–O–C), rather than between lead (Pb) and ether. This process primarily serves to eliminate defect states and stabilize the perovskite surface structure. Thus, 18C6–K⁺ molecule was suggested to be effective in passivating FAPbI₃ surface defects and enhancing the stability of perovskite solar cells.