Growth and properties of cubic SnS films prepared by chemical bath deposition using EDTA as the complexing agent

Abstract

Recently, thin films of cubic SnS emerges as a promising solar cell absorber layer owing to its suitable optical and electrical properties. In this paper, we report the growth of cubic SnS thin films by a chemical bath deposition technique using ethylene diamine tetra-acetic acid (EDTA) as the complexing agent. Optimization of EDTA concentration has been carried out to increase the film thickness and to obtain compact and uniform cubic SnS films with good grain size. SnS films with a thickness in the range 500− 620 nm could be obtained with increasing the EDTA concentration in the solution for a deposition time of 6 h. The X-ray diffraction analysis of these films revealed the presence of cubic SnS with (222) and (400) as the preferred orientations. The lattice parameter of these films is found to be a = 1.158 nm and their crystallite size increases from 46 nm to 60 nm with increase in the EDTA concentration from 0.075 M to 0.125 M. Raman spectroscopy analysis revealed the presence of a minor SnS2 secondary phase in these films. X-ray photoelectron spectroscopy analysis revealed that Sn and S exhibit oxidation states of +2 and −2, respectively in these films. Scanning electron microscopic studies showed that the grain size first increased with increasing EDTA concentration from 0.075 M to 0.10 M and then decreased when the EDTA concentration is further increased to 0.125 M in the solution. The films deposited with an EDTA concentration of 0.10 M are compact and uniform with an average grain size of ∼1 μm. The direct optical band gap of these films, estimated from their spectral transmittance (Tλ) and reflectance (Rλ) data, is found to increase from 1.67 eV to 1.73 eV with increase in the EDTA concentration from 0.075 M to 0.125 M in the solution. Hall Effect measurements showed that the films are p-type in nature. The films deposited with 0.10 M EDTA concentration exhibited higher hole mobility of 28.6 cm2 V−1 s1, resistivity of 1.53 × 105 Ω cm and carrier concentration of 2.86 × 1012 cm−3. The above properties suggest that the films deposited from solution with 0.10 M EDTA concentration could be useful as solar cell absorber layer to obtain reasonable device efficiency.