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
Losses in CuInSe/sub 2/-based thin film monolithic tandem solar cells
Two critical aspects for the development of tandem solar cells using CuInSe/sub 2/-alloy materials are addressed. First a structure for monolithic tandem solar cells using wide and narrow bandgap Cu(InGa)Se/sub 2/-alloys in the top and bottom cells is demonstrated. This structure uses an ITO layer as both back contact to the wide bandgap Cu(InGa)Se/sub 2/ and interconnect to the bottom cell. Three different options for the emitter in the bottom cell are compared. Second, progress on the wide bandgap cell using the Cu(InGa)(SeS)/sub 2/ system is presented, and different loss mechanisms in Cu(InGa)Se/sub 2/ and CuInS/sub 2/ based devices are identified. Efficiency with Cu(InGa)Se/sub 2/ is reduced by lower optical absorption and poor current collection while with CuInS/sub 2/, it is reduced by interface recombination.
A concept of general monotonicity and applications
In this paper we investigate properties of the general monotone sequences and functions, a generalization of monotone sequences and functions as well as of those of bounded variation. Some applications to various problems of analysis are given. © 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim