Comprehensive Characterization of CIGS Absorber Layers Grown by One-Step Sputtering Process

We have demonstrated that the use of a one-step sputtering process allowed for the fabrication of copper indium gallium diselenide (CIGS) thin films by RF magnetron sputtering without an additional selenization process. The CIGS thin films deposited at different substrate temperatures were synthesized on soda-lime glass (SLG) substrates using a single quaternary CIGS target. The film composition ratios of ([Cu]/[In]+[Ga]), ([Ga]/[In]+[Ga]), and ([Se]/[Cu]+[In]+[Ga]) were almost consistent with those of the sputtering target. X-ray diffraction (XRD) and Raman results showed that the crystallinity of the CIGS thin films was gradually improved as substrate temperatures increased. Transmission electron microscopy (TEM) showed that the films grown at 600 °C have a columnar structure with the grain size of ~100 nm. In addition, for the CIGS films grown at 600 °C, TEM-EDX analysis revealed that the synchronized fluctuation of the Cu and Se signals was observed in the direction of the film depth, while the In and Ga signals were constant. As a result, the CIGS solar cell made using the film showed a degraded cell efficiency of 2.5%, which might be have been caused by not only Cu-rich and Se-poor compositions but the locally unstable composition in the CIGS films fabricated by one-step sputtering.