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GROWTH AND CHARACTERIZATION OF TERNARY CHALCOGENIDE THIN FILMS FOR EFFICIENT SOLAR CELLS AND POSSIBLE INDUSTRIAL APPLICATIONS

ABSTRACT 

Ternary thin films of  Iron Copper Sulphide  (FeCuS), Iron Zinc Sulphide (FeZnS), Lead Silver Sulphide (PbAgS), Copper Silver Sulphide (CuAgS) and Copper Zinc Sulphide (CuZnS) were  grown  using cheap and simple solution  growth technique with EDTA,  TEA and NH3  as  complexing agents.  The deposited films were characterized using PYE-UNICO-UV-2102 PC  spectrophotometer,  and  optical microscopy. The results suggest  that some of the films have  crystal structures. From the spectral analysis of absorbance/transmittance, the optical and solid  state properties were deduced. The other optical properties so obtained  include the reflectance,  absorption coefficient, refractive index, extinction coefficient, optical conductivity and thickness, while the solid state properties are dielectric constant and band gap energy.  For all  the five categories of thin films grown (i.e. FeCuS, FeZnS, PbAgS, CuAgS and CuZnS), absorbance was high in UV and low in VIS-NIR-regions, while the transmittance were low in UV-region and high in VIS-NIR-regions. The reflectances  were high in UV-region and low in the VIS-NIR-regions. For FeCuS, FeZnS, PbAgS, CuAgS and CuZnS, the absorption coefficient ranged from 0.1x106 m-1 to 1.65x106 m-1, 0.2x106 m-1 to 2.3x106 m-1, 0.5x106 m-1  to 0.9x106 m-1, 0.5x106 m-1 to 1.28x106 m-1 and 0.24x106 m-1 to 1.6x106 m-1, respectively. The real part of the refractive index ranged from 1.2 to 2.3, 0.72 to 2.3, 0.1 to 2.3, 1.94 to 2.28 and 1.6 to 2.3, respectively. The corresponding values of optical conductivity ranged from 0.03x1014 s-1  to 0.6x1014 s-1, 0.07x1014 s-1, 0.06x1014 s-1  to 0.6x1014 s-1, 0.24x1014 s-1 to 0.6x1014 s-1  and 0.12x1014 s-1  to 0.6x1014 s-1, respectively. The extinction coefficient, ranged from 0.005 to 0.038, 0.004 to 0.056, 0.010 to 0.140, 0.025 to 0.064 and 0.008 to 0.082, respectively. The direct band gap ranged from  2.4eV to2.8eV for FeCuS, 2.9eV for FeZnS, 1.5eV to 2.1eV for PbAgS, 2.3eV for CuAgS and 2.2eV to 2.4eV for CuZnS. The values of the indirect band gap were in the range 0.6eV to 1.0eV for FeCuS, 1.9eV for FeZnS, 0.3eV to 0.8eV for PbAgS, 1.1eV for CuAgS and 0.4eV to 0.9eV for CuZnS.  The real part of the dielectric constant ranged from 1.4 to 5.2, 0.7 to 5.2, 0.4 to 5.2, 3.8 to 5.2 and 2.2 to 5.2, respectively, while the corresponding imaginary part of the dielectric constant ranged from 0.008 to 0.136, 0.008 to 0.164, 0.010 to 0.390, 0.100 to 0.290 and 0.030 to 0.360, respectively.  The range of band gaps,  1.5eV to 2.9eV makes the films suitable for solar cells fabrication; this is in agreement with the finding for the film FeCdS.