| 초록 |
The replacement of the CdS buffer layer is desirable for the development of non-toxic, environmentally friendly kesterite thin-film solar cells (TFSCs). Recently, several ternary compound semiconductors have been extensively investigated as an alternative buffer layer for Cd-free TFSCs. Herein, the effectiveness of (NH4)2S treatment on the surface properties of the absorber as well as the device performance of atomic layer deposited (ALD) Zn(O,S) buffer-based CZTSSe solar cells have been investigated. X-ray photoelectron spectroscopy (XPS) results showed that the elemental compositions of the CZTSSe surface were significantly influenced by (NH4)2S treatment, whereas the surface morphologies of the CZTSSe absorber layers remained unaffected. XPS results also revealed that the (NH4)2S solution treatment substantially removed the native oxide layer from the CTZSSe absorber surface. The fabricated CZTSSe/Zn(O,S) device without (NH4)2S treatment displayed an initial cell efficiency of 7.46%. The energy conversion efficiency was significantly increased to 9.82% after the (NH4)2S treatment of the absorber layers for an optimum duration of 1 min, which is the highest efficiency achieved to date for Zn(O,S) buffer-based kesterite solar cells. The improved device performance is predominantly attributed to the pronounced increase in the fill factor (FF) of the TFSCs resulting from the removal of oxides/hydroxides from the CZTSSe surface and passivation of absorber surface with sulfur species. However, extending the treatment duration to 3 or 5 min resulted in the deterioration of cell efficiency, primarily due to the progressive degradation of the device FF. This study demonstrates a plausible route to improve the performance of Zn(O,S) buffer layer-based kesterite solar cells through simple surface treatment of the absorber layers using (NH4)2S solution. |
