Effect of Dye Extract Volume Variation on the Optical Properties of Spray-Deposited ZnS Thin Films

Abstract

ZnS doped with various volumes of H. Sabdariffa (Zoborodo) dye extracts were deposited onto ultrasonically cleaned soda-lime glass substrate at the substrate temperatures of 200oC using the low-cost and scalable chemical spray pyrolysis technique. The final spray solution for the deposition of the films contained aqueous solutions of ZnSO4.7H2O, SC(NH2)2, and H.Sabdariffa (Zoborodo) dye extracts. ZnSO4.7H2O and SC(NH2)2 served as precursors for Zn2+ and S2- respectively while H.Sabdariffa (Zoborodo) was used as dye. The absorbance measurements were carried out in the wavelength range (400-1100) nm using (HINOTEK 756S UV-VIS) Spectrophotometer. From the analysis of the absorbance’s spectral other optical parameters such as transmittance, reflectance, absorption coefficient, band gap and optical density were calculated. All the films indicated high absorbance in the ultra-violet regions and high transmittance in the entire regions whereas reflectance was generally low in all the regions of electromagnetic spectrum. The values of absorption coefficients were found to be high in the order of 109 m-1. The band gaps of the films were fairly high within of the range 2.33 - 2.81eV.  The optical density indicated range of 0.4 - 9.6.  Based on the high absorbance of the films in the ultra-violet regions, the films are suitable materials for solar thermal applications. The high transmittance of the films across the entire electromagnetic spectrum,  make the films suitable materials for solar control coatings inside buildings.  The  relatively low reflectance of the films in all the regions of electromagnetic spectrum indicate they are suitable materials for anti-reflection coatings such as in the coating of windscreens and driving mirrows to minimize effect of dazzling light from vehicles following behind at night. The high absorption coefficients of the films showed they can be used as an ideal absorber in photovoltaic conversions. The high band gap indicated by the films make them appropriate materials for photovoltaic applications. The optical density values indicated by the films are good for anti-reflection coatings in optics.