Passivation Mechanism of (18-Crown-6) Potassium on Complex Defects in SnO2 Electron Transport Layer of Solar Cells

In this study, first-principles calculations were employed to systematically investigate the interaction mechanisms between (18-crown-6) potassium (18C6-K+) and six typical defect sites on the SnO2 (110) surface, including Sni + SnO, Oi + OSn, VO + Sni, VSn + SnO, VSn + Sni, and Sni. Six intrinsic or complex defects universally coexist on the SnO2 surface, and the defect states they introduced allow for precise tuning of material performance. The results demonstrated that the 18C6-K+ molecule can stably adsorb on all six defect sites and significantly increase defect formation energies, indicating its thermodynamic capability to suppress defect generation. A subsequent density of states (DOS) analysis revealed that the 18C6-K+ molecule exhibits strong defect passivation effects at Sni + SnO, VO + Sni, VSn + Sni, and Sni sites, and partially mitigated the electronic disturbances induced by Oi + OSn and VSn + SnO defects. Furthermore, the incorporation of 18C6-K+ has been shown to reduce the electronic effective mass of defective systems, thereby enhancing surface carrier transport. A subsequent charge density difference (CDD) analysis revealed that the 18C6-K+ molecule forms Sn-ether and O-ether interactions through its ether bonds (C-O-C) with surface Sn and O atoms, inducing interfacial electronic reconstruction and charge transfer. The Bader charge analysis revealed that the H, C, and O atoms in 18C6-K+ lose electrons, whereas the Sn or O atoms at the surface defect sites gain electrons. This outcome is consistent with the CDD analysis and quantitatively confirms the extent of electron transfer from 18C6-K+ to the SnO2 defect regions. These interactions effectively passivate defect states, thereby enhancing interfacial stability. The present study offers theoretical guidance and design insights for the development of molecular passivation strategies in SnO2-based optoelectronic devices.