Desposition of zinc oxide thin films by spin coating and examination of their structural,electrical and optical characteristics for solar cell application

This dissertation reports on the deposition of ZnO prepared by sol-gel on substrates by spin-coating, and the characterisation of the resulting thin films. The precursor solution was synthesized using appropriate quantities of aqueous Zinc Acetate dehydrate, 2- Methoxyethanol and Ethanolamine. The mixing was carried out on a hot plated magnetic stirrer for 2 hours at a temperature of 70oC resulting in a clear solution that was allowed to cool down to room temperature before the coating was commenced.
A coating speed of 3000 rpm was applied for 60 seconds with a looping cycle of one which was followed by preheating at 200oC for 2 minutes. The four samples selected in the study were coated at cycles of six, eight, ten and twelve and were all annealed at a temperature of 500oC for two hours.
After annealing, the samples were then characterised. The samples were greyish in colour. They were also found to be largely amorphous when coated on glass substrates. The grain sizes measured using the Scanning Electron Microscopy (SEM) were found to be 45 nm in diameter. X-ray Diffraction (XRD) shows that the thin films are crystalline in natureand their XRD patterns showing enhanced intensities for the peaks corresponding to (002) plane at 2θ depicting a preferential orientation along the c - axis.
The thickness of the films on substrates measured within the range of 1200nm – 1500nm. Specular ultra-violet visible (UV-vis) measurements gave a direct transition optical band gap energy (Єg) of 3.37eV. The highest transmission peak occurred at 95 percent which is within the range of the best solar cell devices of 95 percent transmission.

In this study crystalline ZnO films with a high conductivity at 5.87×10-4 Ω-1cm-1 and lowest resistivity about 1.7×10-3 Ωcm were obtained. Carrier concentration and Hall Coefficient were to be found 1.26 x 1017cm3 and 2.01 x 10-3 m3/C respectively. These properties are a health indicator that ZnO thin films produced by the sol-gel method can operate as a Transparent Conductive Oxides (TCO).