Segregation-induced co-passivation effect of S and Cl on CdTe grain boundaries

The efficiency of polycrystalline CdTe solar cells can be significantly enhanced through CdCl2 treatment. However, while this treatment promotes the diffusion of sulfur (S) into CdTe, the improvement cannot be solely attributed to chlorine (Cl); S may also play a crucial role. In this study, using first-principles calculations, we investigated the effects of S and Cl co-doping on the electronic properties of CdTe Σ3 (112) Te-core GBs. The Σ3 (112) Te-core GBs present challenges due to deep gap states caused by Te-Te and Cd-Cd wrong bonds. Notably, the segregation behavior of S dopants within the GBs suggests their potential to significantly influence the electronic properties. When co-doped with Cl, it is evident that S is more likely to occupy interstitial sites rather than substituting for Te atoms under Te-rich conditions. The co-passivation of S and Cl at the GBs can eliminate all gap states, thereby enhancing electrical performance. These findings provide insights into the synergistic effects of dopants on GBs and propose a promising strategy to improve the performance of CdTe solar cells through doping.