Comparative study of sputtered and electrodeposited CI(S,Se) and CIGSe thin films

Copper indium disulphide CuInS2 (CIS) and diselenide CuInSe2 (CISe) and their alloys with gallium CuIn1-xGa xSe2 (CIGSe) thin films have been prepared using both high- and non-vacuum processes. The well known two-stage process consisting in a sequential sputtering of Cu and In thin layers and a subsequent sulfurisation has led to the formation of good quality CuInS2 ternary compound. The films exhibit the well known chalcopyrite structure with a preferential orientation in the (112) plane suitable for the production of the efficient solar cells. The absorption coefficient of the films is higher than 104 cm-1 and the band gap value is about 1.43 eV. A non-vacuum technique was also used. It consists on a one step electrodeposition of Cu, In and Se and in a second time Cu, In, Se and Ga. From the morphological and structural point of view, the films obtained are similar to those prepared by the first technique. The band gap value increases up from 1 eV for the CIS films to 1.26 eV for the CuIn1-xGa xSe2 with 0 < x < 0.23. The resistivity at room temperature of the films was adjusted to 10 Ωcm after annealing. The films exhibit an absorption coefficient more than 105 cm-1. The most important conclusion of this study is the interesting potential of electrodeposition as a promising option in low-cost CISe and CIGSe thin film based solar cells processing