Formation of gradient Ga distribution in Cu(In,Ga)Se2 thin-film solar cells prepared by (InGa)2Se3/CuInGaSe2 stacking structure followed by Se-Vapor selenization

Cu(In,Ga)Se2 (CIGS) light absorption layers with gradient Ga distribution were prepared by utilizing the sequential deposition of (InGa)2Se3 (IGS) and CIGS layers. The IGS buffer layers were deposited on Mo/soda lime glass substrate at various working pressures (WP = 1, 10 and 30 mtorr) followed by the deposition of CIGS layers. Afterward, the microstructures and compositions of CIGS layers formed by the selenization of CIGS/IGS stacking layers in Se vapor ambient at 560 °C for 1 h were investigated. The CIGS layer with the optimized microstructure and transport properties was then implanted in the thin-film solar cells and the device with the best conversion efficiency of 8.22 ± 0.0754% was achieved. The satisfactory solar cell performance was ascribed to the insertion of IGS layer which remedies the deficiency of In, Ga and Se elements and forms the gradient Ga distribution in CIGS layer as revealed by the secondary ion mass spectroscopy.