Preparation of Wide Bandgap Cu(InGa)(SeS)2 Solar Cells with Improved Fill Factor
Cu(InGa)(SeS)2 absorber films with a band gap Eg  ges 1.5 eV have been prepared using thermal co-evaporation with different sequences of Cu rich and Cu poor deposition. The composition through the film is, in some cases, non-uniform due to changes in relative S and Se incorporation. The compositional depth profile was characterized by grazing incidence X-ray diffraction and Auger electron spectroscopy with Ar sputtering. The composition ratio [S]/[S+Se] in the films depends on the process and the composition ratio [Cu]/[In+Ga] during deposition. Solar cells with a soda-lime glass/Mo/CIGSS/CdS/ZnO/ITO/(Ni-Al grid) structure were fabricated and a higher FF > 77 % than previous wide bandgap Cu(InGa)(SeS)2 devices has been demonstrated with these processes. The best Cu(InGa)(SeS)2 cell with Eg=1.5 eV is prepared by the two-layer process, and shows an efficiency of 11.2 %, with Voc =0.760 V, Jsc=19.2 mA/cm2, and FF=77.3 %. Quantum efficiency of the CIGSS cells shows relatively poor response for wavelength > 600 nm compared to that with CuInS2
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.
Rotational Analysis of the CrO Bands
The (0, 1), (0, 0) and (1, 0) bands of the CrO, which appear in the red and yellow region, are analysed rotationally, and we have been able to show that these bands owe to the transition 5 Π- 5 Π. We have shown the theoretical formulae for the quintet state, which can be applied in the case of nearly (a), and obtained the molecular constants as follows,