Defect levels in Cu2ZnSn(SxSe1-x) 4 solar cells probed by current-mode deep level transient spectroscopy

Abstract

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 Ev + 0.12 eV, and Ev + 0.32 eV identified as CuZn(-/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 Ev + 0.03 eV corresponding to Cu-vacancy (VCu). Our results revealed that VCu is the primary defect center in the high-efficiency kesterite solar cell in contrast to the detrimental Cu Zn and CuSn antisites found in the low efficiency CZTSSe cells limiting the device performance. © 2014 AIP Publishing LLC.