Preparation of Wide Bandgap Cu(InGa)(SeS)2 Solar Cells with Improved Fill Factor

Cu(InGa)(SeS)₂ absorber films with a band gap E_g 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 E_g=1.5 eV is prepared by the two-layer process, and shows an efficiency of 11.2 %, with V_oc =0.760 V, J_sc=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