This work presents the physical characterization of 1 µm CdTe thin films for photovoltaic applications. 1 µm CdTe films were deposited on well cleaned glass substrates by thermal evaporation technique. The effect of annealing temperatures on morphological, structural and optical characteristics of the crystalline CdTe films was investigated at different annealing temperatures (as deposited, 400 and 500 °C) for 1 hour. The films were characterized with Scanning Electron Microscope (SEM), X-ray diffraction (XRD) and UV-Visible spectrophotometer. The results revealed that the reflectance characteristics of CdTe films are strongly dependent on the wavelength of electromagnetic spectra. The maximum percentage optical transmittance of CdTe films for as-grown, 400 and 500 degrees Celsius annealed films are 59, 60 and 58 % respectively at 800 nm wavelength. The absorbance of the film decreases with increases in wavelength and found to be 1.65, 1.25 and 0.85 % for the as-grown, 400 and 500 degrees Celsius annealed films respectively. The absorption coefficient exhibits higher values in the shorter wavelength and decreases as the wavelength increases in the visible region of the solar spectrum. The value also decreases with the increases in annealing temperature. High absorption coefficients of 3.9×104, 2.9×104 and 1.9×104 occurred at 400 nm wavelengths for the as-grown, 400 and 500 degrees Celsius annealed CdTe films respectively. The scanning electron microscope studies showed that the films are homogenous and free from crystal defects. The annealing temperatures affect the grain sizes and the band gap. The optical energy band gap is found to be increasing as the annealing temperatures increases. The optical energy band gaps of 1.5, 1.65 and 1.8 eV were obtained for as-grown, 400 and 500 degrees Celsius annealed CdTe films. The obtained results revealed that 1 µm CdTe film may be used as absorber layer in CdS/CdTe thin film solar cells due to its band gap.
Key words: CdTe, glass substrate, thermal evaporation, annealing temperature, Energy band gap
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