Open Access

ARTICLE

Characterization of Undoped Spray-Deposited ZnO Thin Films of Photovoltaic Applications

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1 Physics Department, Faculty of Science, University of Jordan, Amman, Jordan.

Fluid Dynamics & Materials Processing 2010, 6(2), 165-178. https://doi.org/10.3970/fdmp.2010.006.165

Abstract

Undoped polycrystalline ZnO thin films were produced on glass substrates at a substrate temperature Ts= 450 C by the spray pyrolysis (SP) technique. The films were characterized by analyzing their I-V curves, transmittance, X-ray diffractograms (XRD) and their scanning electron microscope (SEM) images. The I-V plots are all linear and the resistivity was found to be about 200W.cm. The transmittance in the visible and near infrared regions is as high as 85% which is suitable for solar cell applications. The absorption coefficient which is deduced from the transmittance measurements is continuously increasing with the photon's energy and it rapidly increases around and after the absorption edge. In the low energy side the absorption coefficient shows the exponential behavior which is known as Urbach tailing, that is related with localized states. The width of the tail was predicted and found to be 0.969 eV. By assuming a direct optical transition, the bandgap energy was estimated and found to be about 3.27 eV. X-ray diffraction patterns revealed that the films have a hexagonal wurtzite structure and that they are highly ordered with a preferential orientation (002). The grain size was estimated by using Scherrer formula and found to be 30 nm, which means that the films have a nanocrystalline nature. The presence of very weak lines in the XRD diffractograms is evidence on the presence of nanocrystallites of much smaller size than the estimated one. The SEM image shows that the surface is uniform and completely covered with material. The grains appearing in the SEM micrograph have a much greater size than that estimated from XRD diffractograms which means that they are aggregates of much smaller crystallites.

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