Preparation of Cu(In,Ga)Se-2 thin films from In-Ga-Se precursors for high-efficiency solar cells

Growth of Cu(In,Ga)Se-2 (CIGS) films from In-Ga-Se precursors was character ized by scanning Auger electron spectroscopy (SAES), secondary ion mass spe ctroscopy (SIMS), x-ray diffraction, scanning electron microscopy, and tran smission electron microscopy (TEM). In-Ga-Se precursor layers were deposite d on Mo-coated soda-lime glass, and then the layers were exposed to Cu and Se fluxes to form CIGS films. The SIMS and SAES analyses showed a homogeneo us distribution of Cu throughout the CIGS films during the deposition of Cu and Se. The phase changes observed in the CIGS films during the deposition of Cu and Se on the In-Ga-Se precursor films were as follows: (In,Ga)(2)Se -3 --> [Cu(In,Ga)(5)Se-8] --> Cu(In,Ga)(3)Se-5 --> Cu(In,Ga)Se-2. The grain size increased from the submicron grains of the (In,Ga)(2)Se-3 precursor f ilm to several micrometers in the stoichiometric Cu(In,Ga)Se-2 film. A grow th model of CIGS crystals is introduced on the basis of the results of TEM observations. CIGS crystals are mainly grown under (In,Ga)-rich conditions in the preparation from In-Ga-Se precursor films.