Influence of growth process on optical properties of Cu(In1 − xGax)Se2 thin film solar cells

The influence of the conventional depositing processes on the optical properties of Cu(In,Ga)Se2 (CIGS) thin films in solar cell structures was investigated by measuring the photoluminescence (PL) and Raman spectra of the CIGS layer at each stage of the solar cell deposition process. The intensities of the PL and the Raman A1 mode increase after the CdS buffer layer is deposited, suggesting that the CdS layer either improves the optical quality of the CIGS film or protects it from degradation due to environmental factors. The temperature and excitation power dependences of the PL for the bare CIGS sample are very different from those for the samples with the CdS layer, reflecting different characters of the luminescence centers near the surface of the CIGS layer. On the other hand, the lateral homogeneity, as seen in the micro-PL and micro-Raman images, does not seem to improve. After the ZnO window layer is deposited, the overall PL and Raman intensities do not change much, although the intensity distribution becomes more inhomogeneous.

► Study of Cu(In,Ga)Se2 (CIGS) thin film homogeneity in CIGS, CdS/CIGS, and ZnO/CdS/CIGS.
► CdS layer either improves the CIGS film or protects it from degradation.
► CdS or ZnO layer does not improve the homogeneity of CIGS appreciably.