Spectroscopic imaging study on CIGS thin film solar cells

Cu(In_1-xGa_x)Se (CIGS) based thin film solar cells are usually built by depositing CdS as a buffer layer and ZnO as a window layer on top of the CIGS absorber layer. In order to optimize their performances, it is essential to understand the interactions between the layers. In this study, we have investigated the interactions between the layers by examining the optical properties of the CIGS solar cell structure at each step of the fabrication process-CIGS, CIGS/CdS, and CIGS/CdS/ZnO- using photoluminescence and Raman spectroscopic imaging techniques. The images of the intensity of the Raman peak at 175 cm^-1 due to the A₁ vibration mode show that the homogeneity improves after CdS deposition. Micro-PL intensity imaging also confirmed this observation. Furthermore, the PL peak intensity and the energy position vary after each layer deposition.