Interfacial Passivation of Kesterite Solar Cells for Enhanced Carrier Lifetime: Ab Initio Nonadiabatic Molecular Dynamics Study

Nonradiative recombination at the front contact interface of kesterite solar cells hinders the extraction of photo‐generated carriers, significantly restricting the efficiency enhancement. However, identifying the recombination centers and proposing effective passivation strategies remain open questions. First‐principles calculations combining with nonadiabatic molecular dynamics (NAMD) simulations unveil that the interfacial translational symmetry breaking in elemental valence states leads to a detrimental donor‐like Cu2ZnSnS4/CdS interface with deep states originating from the interfacial Sn‐5s orbital, which serve as significant nonradiative recombination centers. Here, two mechanisms are proposed for eliminating the deep interface states: 1) directly replacing Sn‐5s with higher outer orbital levels by substituting group IIIA elements (In and Ga) for the interfacial Sn atom; 2) introducing an extra defect‐level coupling with Sn‐5s by substituting group VA elements (N, P, and As) for the S atoms bonded with the interfacial Sn atom. The representative InSn and PS acceptor defects, which are energetically favorable at the detrimental donor‐like interface, effectively passivate the deep interface states, markedly improving the carrier lifetimes by weakening nonadiabatic coupling between the band edge and the interfacial states. This study reveals the origin of the interfacial nonradiative recombination of kesterite solar cells and offers insights into interfacial passivation in semiconductor devices. The deep interface states of Cu2ZnSnS4/CdS heterojunction in kesterite solar cells are identified as the interfacial Sn‐5s orbital due to translational symmetry breaking in the elemental valence states, which are successfully passivated by two mechanisms: cation or anion substitution to elevate the original deep state or introduce extra defect level coupling with it, enhancing the carrier lifetimes.