Structural and optical properties of Cu2SnS3 sprayed thin films
Introduction
The ternary compound semiconductor of copper indium disulfide CuInS2 is an important material which has been investigated for its numerous applications especially as an absorber material in solar cells. This ternary material has a band gap of 1.55 eV [1] which borders the optimum value necessary for conversion of a solar spectrum. Thin film cells based on this material (ZnO/CuInS2) have been reported to show efficiencies as high as 11.4% [2].
Due to the increasing price of indium the development of new photovoltaic ternary sulfides are in demand. Replacing indium by tin, semiconducting copper tin sulfides such as Cu2SnS3, Cu3SnS4 and Cu4Sn7S16 [3] could be candidates to play an important role in the energy conversion domain in the future. To date, a few works on the preparation of Cu2SnS3 thin films have been reported [4], [5], [6], [7], [8], [9], [10]. However, no attempts have been made to prepare it by simple, costless and large-area chemical procedure.
The present work reports for the first time, the preparation and the physical characterization of Cu2SnS3 thin films on Pyrex glass substrates by an annealing process under a sulfur atmosphere from a sandwich layers of SnS2 and CuxS (1 ≤ x ≤ 2) obtained by the spray pyrolysis technique. The main idea is to benefit from the mobility of the copper in copper sulfide film [11]. Thus, the superposition of CuxS and SnS2 leads in principle to a new material after an appropriate annealing process of these films.
Section snippets
Films preparation
SnS2 and CuxS thin films were consecutively deposited on 20 × 10 × 2 mm3 Pyrex glass substrates by spraying an aqueous solution (a mixture of water and methanol) containing thiourea (SC(NH2)2; 0.6 M) and tin chloride (SnCl4; 0.2 M) for the first thin film whereas the second one is obtained using a solution containing thiourea (2.10− 2 M) and copper (II) chloride (CuCl2,2H2O; 10− 2 M) as precursors. The substrate temperature equal to 280 °C was chosen to obtain SnS2 thin film, because in our
Structural study
Fig. 1a, b and c shows the diffraction spectra of SnS2, CuxS and SnS2/CuxS thin films grown separately on Pyrex glass substrates by the spray pyrolysis system at 280 and 300 °C for SnS2 and CuxS materials respectively. Moreover, the spectrum related to SnS2 film depicts a well defined peak of (001) principal orientation corresponding to β-SnS2 material as reported elsewhere [12] whereas the spectrum related to CuxS thin film (Fig. 1b) shows on the contrary peaks corresponding to a mixture of
Conclusion
The copper tin sulfide films have been grown by the spray pyrolysis technique followed by an annealing process. Structural, morphological and optical properties were studied. It has been found that the material is p-type with grains preferentially (111) oriented of Cu2SnS3 crystallizing in a cubic structure. The deposited films showed a relatively high absorption coefficient of ~ 104 cm− 1 and exhibited a direct transition gap of about 1.15 eV. In the same line, electrical measurements are in
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