Structural investigation of the back contact in CIGSe solar cells with Li-doped NiO hole transport layer

Abstract In recent years, the increase in the conversion efficiency of CIGSe solar cells has plateaued, necessitating improvements of back contact properties for further efficiency gains. In this study, we conduct a structural analysis of the back contact to investigate the feasibility of applying Li-doped NiO as a hole transport layer in CIGSe solar cells. X-ray diffraction and atomic force microscopy analyses demonstrate that CIGSe grown on NiO:Li exhibits crystallinity comparable to that grown on Mo. However, TEM and EDS mapping images of the Mo/NiO:Li/CIGSe structure reveal significant interlayer diffusion, leading to the formation of secondary phases such as GaO x , which are attributed to the high deposition temperature of ≈550 °C required for the CIGSe layer. To mitigate this issue, a SiO 2 barrier layer is introduced, effectively reducing atomic diffusion across the Mo/NiO:Li/CIGSe interfaces and better preserving the back-contact structure.