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Abstract: Films of copper sulfides with various composition and properties were deposited on FTO (fluorine doped tin oxide) substrate using SPD (Spray pyrolysis deposition) as deposition technique, from aqueous and alcoholic solutions. The precursors' solutions of copper (II) chloride and thiourea, in different Cu:S ratios, were sprayed and the deposition parameters were varied. The present paper studies the electrical conductivity of the as-deposited films. The influence of temperature, film composition and film thickness was investigated. Electrical measurements (I-V curves) were registered in dark and were correlated with the film composition and structure, as obtained from the XRD patterns.
Key words: copper sulphide, thin films, Spray pyrolysis deposition.
1. Introduction
It is known that CuxS are useful minerals therefore their mineralogical and technological properties were extensively studied. Recently, CuxS thin films have attracted the attention of researchers due to their optical and electrical properties. The optical spectra of CuxS films exhibit high transmission in the visible region and absorption throughout the near-infrared region (800-1500 nm) [5]. The compound exhibits fast ion conduction at higher temperatures and exists in a wide variety of compositions ranging from Cu2S at copper-rich sites to CuS2 at the copperdeficient sites such as CuS [1].
From the eight copper sulfides that have been discovered with different stoichiometries only five of them are stable at room temperature: CuS (covellite), Cu1.75S (anilite), Cu1.8S (digenite), Cu1.96S (djurleite), Cu2S (chalcocite). Considering its pre-eminent role in thin film CuxS/CdS solar cells, copper sulphide has been investigated [2] in both bulk single-crystal and thin film form with regard to its structural, optical and electronic properties. These properties are largely determined by the composition of CuxS which, in turn, is governed by the preparation method and deposition conditions applied during growth.
Various processes for producing cuprous sulphide for solar cells have been investigated. These include evaporation of cuprous sulphide powder, flash evaporation of Cu2S, sulphurization of copper foils and films, deposition from a slurry, spray techniques and chemiplating of CdS in CuCl solution [6-7]. All these methods have several...