Effect of Thermal Treatments on Functional Groups and Photometric Measurement of Thermally Evaporated CdS Films for PV Applications

Abstract

This paper investigated the effects of thermal treatments on the functional groups and optical properties of thermally evaporated CdS films for photovoltaics applications. The synthesized CdS nano-particles were evaporated from Molybdenum boat and deposited on clean glass substrates as thin films form. 100 nm CdS films were ensured on glass substrates via thermal evaporation in a residual pressure of 10-5 Torr and substrates at room temperature. The obtained CdS films were annealed at 400 and 500 oC respectively. All samples were characterized using UV-VIS Spectrophotometer. The absorbances of the films were calculated from the transmittance data using Beer's Lambert law. ALPHA II FTIR Spectrometer was employed to investigate the vibrations of the functional groups of CdS films at the respective annealing temperatures under study. Powder X-ray Diffraction (PXRD) was used to confirm the phase of the CdS prior to and after the deposition. The results revealed maximum transmittances of about 90% for all samples at 656, 657 and 646 nm wavelengths respectively and varied at other wavelengths. The vibrations of the functional groups of CdS films were not perturbed by the annealing temperatures under study and the energy band gaps of 2.42, 2.4 and 2.9 eV were estimated for the as grown, 400 and 500 oC CdS films respectively. Based on the obtained results, 100 nm CdS film deposited via thermal evaporation and annealed at 400 oC is hereby encouraged for the development of CdS/CdTe poly crystalline thin film solar cells.