Adjusting the SnZn defects in Cu2ZnSn(S,Se)4 absorber layer via Ge4+ implanting for efficient kesterite solar cells

The power conversion efficiency of kesterite solar cells increases from 9.15% to 11.48% due to the suppression of Sn Zn deep defects by implantation of Ge into CZTSSe absorber layer. • Ge 4+ were introduced into Cu 2 ZnSn(S,Se) 4 (CZTSSe) films to improve the quality of the absorber layer. • The density of Sn Zn deep traps in CZTSSe absorber layer decreased from 8.97 × 10 13 cm −3 to 9.42 × 10 12 cm −3 . • The grain growth of CZTSSe films was promoted due to isovalent cation-substitution with Ge. • Efficiency of CZTSSe solar cells improved from 9.15 to 11.48% mainly owing to the 41 mV V oc increment. The development of kesterite photovoltaic solar cells has been hindered by large open-circuit voltage ( V oc ) deficit. Recently, Sn Zn deep point defect and associative defect cluster have been recognized as the main culprit for the V oc losses. Therefore, manipulating the deep-level donor of Sn Zn antisite defects is crucial for breaking through the bottleneck of present Cu 2 ZnSn(S,Se) 4 (CZTSSe) photovoltaic technology. In this study, the Sn Zn deep traps in CZTSSe absorber layer are suppressed by incorporation of Ge. The energy levels and concentration of Sn Zn defects measured by deep-level transient spectroscopy (DLTS) decrease significantly. In addition, the grain growth of CZTSSe films is also promoted due to Ge implantation, yielding the high quality absorber layer. Consequently, the efficiency of CZTSSe solar cells increases from 9.15% to 11.48%, largely attributed to the 41 mV V oc increment.