Growth and properties of Cu(In, Ga)(S, Se)2 films

Cu(In, Ga)(S, Se)₂ (CIGSSe) films were grown on Mo/soda-lime glass substrates in a three-stage process using a molecular beam epitaxy apparatus equipped with an rf-cracked S-radical beam source. CIGSSe films have been studied for their application in the development of solar cells with wide-bandgap semiconductors. The S/(S+Se) composition ratios in the fabricated films were determined from electron probe microscopy analysis (EPMA), and scanning electron microscopy (SEM) images of the films were obtained. The results showed that the grain sizes in the films decreased with increasing S concentrations. The surfaces of the films with higher S/(S+Se) composition ratios had greater roughness. To determine the compositional depth profile of the films, the acceleration voltage dependencies of EPMA on the S/(S+Se) ratios, and the group-VI atoms (S and Se) were obtained. The fabricated CIGSSe solar cell achieved an efficiency of 15% and had a fill factor of 0.72. However, since the open circuit voltage was lower than the expected value improvement in the band profile is necessary.