Effect of Concentration on Morphological, Optical and Electrical Properties of Copper Doped Zinc Oxide Thin Films Deposited by Electrostatic Spray Pyrolysis (ESP) Technique

Pure zinc oxide (ZnO) and copper (Cu) doped ZnO thin films were synthesised from the precursor’s
concentrations (zinc acetate and copper acetate) onto glass substrate via electrostatic spray pyrolysis
(ESP) deposition technique at 350°C in air ambient with different Cu doping concentrations (0%, 5%,
10%, 15% and 20%). The thin films were analysed with regards to its morphological, optical, and
electrical properties before and after annealing. The results indicate that the annealing of the thin films
leads to improved surface morphology and better crystallinity quality. Nanofibers were observed
around the nucleation centre in the pure ZnO thin films. The absorbance was recorded in the
wavelength range of 230 nm to 1100 nm, and the optical transmission of the films was found to
increase for increasing doping concentration of Cu up to 370 nm and then decreased for higher
wavelengths. ZnO:Cu films displayed high optical transparency which is around 86% - 98% in the
visible and infrared regions but minimum in the ultraviolet region. The band gap energy value of the
pure ZnO films was found to be 3.20 eV, whereas the doped films revealed a continuous decreases
for higher doping of Cu concentration, reaching a value of 2.66 eV. The refractive index of the films
significantly changes with the deposition parameter and increases sharply from 1.4597 to 1.7865 and
the highest electrical resistivity was found to be 8.83 μm, and the lowest optical conductivity of 0.113
MƱm-1 was observed in the films with 20% Cu doped film, which indicates that the deposited films are
highly suitable for photovoltaic cells and other optoelectronic device applications.