Preparation and characterization of spray deposited Sn-doped ZnO thin films onto ITO subtracts as photoanode in dye sensitized solar cell

Transparent and conducting thin films of pure and Sn-doped ZnO (ZnO.Sn) were deposited onto ITO coated glass substrates by spray pyrolysis technique at 350 degrees C. Structural, morphological, optical, and electrical properties of the as-prepared thin films were characterized by X-ray diffraction, atomic force microcopy (AFM), Transmission electron microscopy, UV-Vis spectroscopy and photoluminescence, as well as Hall Effect, respectively. The results indicated that all the films were polycrystalline with a hexagonal wurtzite structure exhibiting preferential orientation along (002) direction up to 1 at.% of Sn and random orientation for higher doping. AFM study revealed that the grain size and roughness of the films decreased with increasing Sn doping concentration. The optical gap increased slightly from 3.37 to 3.48 eV due to Burstein-Moss effect. PL spectra showed a strong UV emission peak and a relatively weak green emission peak reflecting the crystalline nature and less oxygen defects, respectively. The electrical conductivity increased with increasing Sn doping concentration, but for higher doping concentration (>1 at.%), the conductivity decreased. The power conversion efficiency of DSSCs based on Sn doped-ZnO thin film exhibited higher efficiency (0.74 %) compared to pure ZnO film because of its large surface area for adsorption of dye molecules. This result indicates that Sn-doped ZnO film has promising application in the field of DSSCs, and the optimization of porous film fabrication condition is efficient for the improvement of ZnO based DSSCs performance.