Electrodeposition mechanism of indium sulfide and indium oxi(hydroxi)sulfide thin films from in(III)-thiosulfate acidic aqueous solutions

The electrochemical deposition of indium sulfide layers is investigated with the aim of replacing cadmium sulfide layers in copper-indium-gallium diselenide thin film solar cells. In this paper the deposition conditions are first investigated from theoretical solution chemistry analysis. Experiments are then carried out using Mo-coated glass conducting substrates and gold-coated electrochemical quartz crystal microbalance. Indium chloride acidic aqueous solutions (pH ∼ 3.5-4) containing thiosulfate ions as the sulfur source are used. Cyclic voltammetry studies are carried out. A potential domain is determined which allows to deposit compact layers. XPS analysis indicates the presence of both sulfur and oxygen in the films. The double structure of the O 1s spectra and the particular S 2p energy dispersion suggest two distinct chemical environments for indium whose respective prominence depends on the deposition potential. At low overpotential, an indium sulfide layer containing oxygen species (O, OH) is predominantly identified whereas at more negative potentials a second environment attributed to the presence of sulfate-type (SO _x) groups emerge. These results are discussed in relation to solution chemistry analysis and possible reaction paths are proposed.