Two-step selenization of Cu-In-Ga precursors for CIGS thin-film solar cells by using a Se cracker

Cu(In1-xGax)Se2 (CIGS) thin-film solar cells have been fabricated using the CIGS compound prepared with a two-step selenization process at 400 .deg. C followed by successive thermal annealing at 550 .deg. C. The compositions of the Cu-In-Ga precursors were controlled by changing the thickness ratio of the Cu-In and the Cu-Ga films. After the selenization, the thickness of the CIGS film was approximately three times that of the precursor layer. X-ray diffraction peaks showed that the CIGS had the chalcopyrite structure with a preferential orientation in the (112) direction. The composition analysis using X-ray fluorescence revealed that the Cu/[III] and the Ga/[III] ratios of CIGS changed in ranges of 0.66 ∼ 0.80 and 0.11 ∼ 0.20, respectively, with variations in the precursor thickness. We obtained a power conversion efficiency of 3.91% from the fabricated CIGS solar cell.