S. Belgacem

Physico-chemical characterization of spray-deposited CuInS2 thin films

Abstract CuInS 2 thin films have been deposited by spray pyrolysis. X-Ray diffraction spectra show that a substrate temperature T s ≥590 K with a ratio of the concentration in the pulverized solution of [Cu]/[In]=1.1 permits well crystallized thin films with a preferential orientation along the (112) direction to be obtained. Scanning electron micrographs of the cross-sectional and top views of the surface show evidence of the good homogeneity of the films. Microprobe analysis as well as X-ray photoelectron spectroscopy show that an almost stoichiometric composition is obtained. In the best films only 3–8 at.% of oxygen is present, which is very promising for such a simple growth technique. Moreover, the oxygen present in the films segregates at the grain boundaries since there is not any significant variation of the interplanar spacing and the optical band gap with the presence of oxygen. The optical band gap values (1.45 eV) increases slightly with the crystalline state.

Evolution of the properties of spray-deposited CuInS2 thin films with post-annealing treatment

CuInS2 thin films have been deposited by chemical spray pyrolysis at 650 K and heat-treated under a sulfur atmosphere for 1 h at the same temperature. The effect of this treatment on the properties of the films was studied by X-ray diffraction, electron microprobe analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, optical and electrical measurements. The changes in the properties, mainly the electrical, are attributed to the fact that the oxygen, originally present at the grain boundaries and linked to indium, is replaced by sulfur: the In2O3 is then removed from the grain boundaries. The treated films are therefore more suitable for solar cell applications, where transversal parasitic effects are an important issue.