Defect levels in Cu₂ZnSn(S_xSe_1−x)₄ solar cells probed by current-mode deep level transient spectroscopy Available to Purchase

Defect levels in kesterite Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells have been investigated by current-mode deep level transient spectroscopy. Experiments were carried out on two CZTSSe cells with photoconversion efficiencies of 4.1% and 7.1% measured under AM 1.5 illumination. The absorber layer of the 4.1% efficiency cell was prepared by annealing evaporated ZnS/Cu/Sn stacked precursor under S/Se vapor, while the absorber of the 7.1% efficiency cell was prepared by co-evaporation of the constituent elements. The 4.1% efficiency CZTSSe cell with a S/(S + Se) ratio of 0.58 exhibited two dominant deep acceptor levels at E_v + 0.12 eV, and E_v + 0.32 eV identified as Cu_Zn(-/0) and Cu_Sn(2-/-) antisite defects, respectively. The 7.1% efficiency cell with purely Se composition S/(S + Se) = 0 showed only one shallow level at E_v + 0.03 eV corresponding to Cu-vacancy (V_Cu). Our results revealed that V_Cu is the primary defect center in the high-efficiency kesterite solar cell in contrast to the detrimental Cu_Zn and Cu_Sn antisites found in the low efficiency CZTSSe cells limiting the device performance.