DEVICE AND MATERIAL CHARACTERIZATION OF CU(INGA)SE-2 SOLAR-CELLS WITHINCREASING BAND-GAP

Thin-film solar cells have been fabricated from Cu(InGa)Se-2 films whi ch were deposited by four-source elemental evaporation with [Ga]/([In] +[Ga]) from 0.27 to 0.69 corresponding to a band gap from 1.16 to 1.45 eV. The films were intentionally deposited with no grading of the Ga and In to avoid gradients in their electrical and optical properties. X-ray diffraction, energy-dispersive x-ray spectroscopy, and Auger ele ctron spectroscopy show that the films have uniform composition with n o change in structure and morphology. Glass/Mo/Cu(InGa)Se-2/CdS/ZnO de vices have open-circuit voltage increasing over the entire band gap ra nge to 788 mV and 15% total area efficiency for band gap less than 1.3 eV, or [Ga]/([In]+[Ga]) less than 0.5. A decrease in device efficienc y with higher Ga content is caused primarily by a lower fill. factor, Analysis of current-voltage and quantum efficiency measurements show t hat this results from a voltage-dependent current collection.