Effects of absorber and front interface defects on the performance of Cu2ZnSn(S, Se)4 solar cells

Substantial defects within the absorber layer and at the front interface of Cu2ZnSn(S, Se)4 (CZTSSe) solar cells have been identified as the primary factor limiting further performance enhancement. This study systematically investigated the correlation between device performance and defect properties (type, capture cross section (σ), energy level (Et), and concentration (Nt)) in both the absorber layer and front interface. Our findings reveal that photovoltaic performance significantly depends not only on defect localization and fundamental parameters (σ, Et, Nt) but also critically on defect type. When acceptor defects dominate the front interface, the device performance remains substantially inferior to that of systems with neutral or donor defects, regardless of other defect parameter variations, primarily attributed to severe open-circuit voltage (VOC) and short-circuit current density (JSC) degradation. Conversely, donor defects in the absorber layer coupled with Nt variations at both interfaces and in the absorber lead to diminished performance compared to neutral or acceptor defects, mainly through VOC and fill factor (FF) deterioration. Notably, the performance responses to alterations in σ and Et demonstrate minimal dependence on the absorber layer defect type. This mechanistic understanding establishes a theoretical foundation for implementing experimental strategies to mitigate defect-induced performance losses in CZTSSe photovoltaics.