Structural, Optical and Electrical Properties of ZnO Thin Films Prepared by Spray Pyrolysis: Effect of Precursor Concentration

ZnO thin films have been prepared using zinc acetate precursor by spray pyrolytic decomposition of zinc acetate on glass substrates at 450 °C. Effect of precursor concentration on structural and optical properties has been investigated. ZnO films are polycrystalline with (002) plane as preferential orientation. The optical transmission spectrum shows that transmission increases with decrease in the concentration and the maximum transmission in visible region is about 95% for ZnO films prepared with 0·1 M. The direct bandgap value decreases from 3·37 to 3·19 eV, when the precursor concentration increases from 0·1 to 0·4 M. Photoluminescence spectra at room temperature show an ultraviolet (UV) emission at 3·26 eV and two visible emissions at 2·82 and 2·38 eV. Lowest resistivity is obtained at 2·09 Ω cm for 0·3 M. The current– voltage characteristic of the ZnO thin films were measured in dark and under UV illumination. The values of photocurrent and photoresponsivity at 5 V are increased with increase in precursor concentration and reaches to maximum value of 1148 μA and 0·287 A/W, respectively which is correlated to structural properties of ZnO thin films.