Annealing time effect on CIGS thin films

Chalcopyrite copper indium gallium (di)selenide (Cu(In, Ga)Se2 (CIGS)) thin film has been examined as an absorber layer for solar cells because of its suitable absorption value, stability and economy in manufacture. CIGS thin films belong to the I-III-VI2 group of the periodic table with the appropriate direct bandgap (1.5 eV). In this study, CIGS thin films were annealed at ∼200°C for four different annealing times (15, 30, 45 and 60 min) to investigate the effect of the annealing time on the crystalline structure and optical properties of CIGS thin films prepared by using the sol-gel dip-coating technique. CIGS thin films annealed at ∼200°C for 60 min were found to have the best structural and optical properties in this study. As the crystallite size increased with the rise in the annealing time, the lattice strain decreased, indicating the elimination of crystallite defects in the CIGS thin-film structure. Hence, the structural changes affected the optical properties slightly and the rise in the optical absorbance (A%) resulted in a decrease in the optical transmittance (T%).