Optoelectronic characterizations of vacuum evaporated Cu₂SnS₃ thin films for device application..

Abstract

The search for new materials suitable for application in photovoltaic cell necessitates the growth of non-toxic, cheap earthly abundant, ternary compound of Cu₂SnS₃ thin film. Thin films of Cu₂SnS₃ semiconductors were prepared by thermal evaporation and sulphurization techniques in vacuum. The bi-layer of Cu-Sn precursors was deposited on cleaned microscopic glass substrate at controlled thickness of 100nm, 500nm and 1000nm and at different substrate temperatures of 27⁰, 100⁰C and 200⁰C.The bi-layer of Cu-Sn was sulphurized in a custom-built reactor for 1hour at 4000C to form Cu₂SnS₃ ternary films. The structure and morphology characteristics of Cu₂SnS₃ ternary film were investigated by X-Ray Diffraction and Scanning Electron Microscope. Four point probe and semiconductor characterization system were used to determine the electrical properties of the deposited Cu₂SnS₃ ternary films. UV –Vis Spectrophotometer measured the optical characteristics of the Cu₂SnS₃ ternary film. The film samples deposited at 270C and at thickness of 100nm and 500nm yielded Cu₂SnS₃ ternary film .The grain size of deposited Cu2SnS3 ternary film is about 1μm and the films were rough (Average Roughness, Ra = 3133.50nm and Root Mean Square, Rq = 3942.60nm). The elemental composition of the film as determined by Energy Dispersive X-Ray System (EDS) are Cu (24.89%), Sn (15.82%), S (16.29%) and artefacts such as Na, Si, Mg and O.The surface profiler shows that the deposited Cu₂SnS₃films are rough. Monoclinic, Cu₂SnS₃ [-1 3 1] at peak 2Ѳ = 28.4⁰ and Anorthic Cu₂SnS₃ [-2 0 10 ] at peak 2Ѳ = 47.25⁰ were identified. The electrical resistivity, ρ, of the Cu₂SnS₃ ternary film is 2.55 x 10^-3 Ω-cm. The Energy band gap, Eg, of the deposited Cu₂SnS₃ film is 1.65eV, Refractive Index, n is 1.14, Extinction Coefficient, K,is 5.27 x 10⁹ and Optical Conductivity , σ0 is 6.74708E+16 Ω^-1cm^-1. These results clearly show good potentials of deposited Cu₂SnS₃ ternary film as an abundant, cheap, non-toxic absorber layer of photovoltaic solar cell.

Key words: Vacuum Evaporation, Sulphurization, Energy band gap, Absorber layer, solar cells.