Origin of Broadband Emission and Large Stokes Shift in Antimony Trisulfide

The antimony trisulfide (Sb₂S₃) has been theoretically predicted to have various merits in exploiting high-performance thin-film solar cells and attracted intense attention. However, the power conversion efficiency of Sb₂S₃-based solar cells is yet to be satisfactory in experiments and the origin of large open circuit voltage (V_OC) loss is still a controversial question. Based on first-principles calculations, we have systematically analyzed the excited state behavior and dynamics images of carriers in Sb₂S₃ materials. Our calculations showed that intrinsic defects like vacancy (V_Sb and V_S) and antisites (Sb_S and S_Sb) are energetically accessible. More importantly, we found that the sulfide vacancy-bound excitons can produce a large Stokes shift of ∼0.66 eV, which could well rationalize the experimental observations like the reduction of V_OC. These new findings suggest that the performance of Sb₂S₃-based solar cells might be largely enhanced by avoiding sulfide vacancy defects.