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