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
Five-source PVD for the deposition of Cu(In1−xGax)(Se1−ySy)2 absorber layers
A new five-source PVD system was developed for the deposition of Cu(In 1-x Ga x )(Se 1-y S y ) 2 (CIGSS) thin films. The system allows the independent and controlled deposition of all five elements. In the first part of this paper, we investigate CIGSS formation via a double-layer process of depositing a Cu-S or Cu-Se layer on top of an In-Ga-Se or In-Ga-S layer, respectively. Incomplete intermix of two different chalcopyrite species is observed. In one case, additionally, an enrichment of Ga at the interface between those two layers is observed. In the second part of the paper, films within the complete compositional range of 0<x<1, and 0<y<1 were deposited on Mo-coated soda lime glass. The incorporation of sulfur in the films depends strongly on the sulfur concentration in the vapor phase, the substrate temperature, and the Cu/In ratio. The films were analyzed by means of EDS, XRD, Rutherford backscattering spectroscopy (RBS), and AES. Solar cells were fabricated and characterized by I-V measurements. We show results for a series of solar cells deposited group-III rich on the equal-gap line E gap =1.5 eV for various S and Ga contents. The best cells show an efficiency near 10%. The highest open circuit voltage is 854 mV at sulfur contents of S/(Se+S)=0.26.
An experimental characterization of roll hemming process
Roll hemming is analyzed for flat surface-straight edge sheets to illustrate how defects and forces behave. The analysis of defects is carried out trough illustrative models to emphasize the main variables of the process. A testing rig to investigate the process is designed and built. Experimental tests are carried out to measure how forces influence final quality part and the experimental data is analyzed and discussed to relate it with main parameters and defects.