Effect of Ammonium Acetate Concentration on the Structural and Optical Properties of CdS Thin Film Grown by Chemical Bat
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Effect of Ammonium Acetate Concentration on the Structural and Optical Properties of CdS Thin Film Grown by Chemical Bath Deposition Technique Hamda A. Al-Thani1, Abeer A. Al Yafeai1, and Falah S. Hasoon1 1 National Energy and Water Research Center (NEWRC), POBOX 54111, Abu Dhabi, UAE ABSTRACT This study focuses on understanding the influence of incorporating Ammonium Acetate into the chemical bath used for the deposition of CdS thin films, on its optical, morphology, and microstructural properties. Thus, CdS thin films were deposited on 1” × 2” microscopic glass substrates using chemical bath deposition (CBD) technique. The deposition process was carried out in a double jacket beaker with fixed chemical bath temperature of 90qC for a deposition time of 40 min. The chemical bath solution consisted of fixed concentrations of Cadmium Acetate, Thiourea, and Ammonium Hydroxide; with corresponding values of 4.8×10-4M; 0.97×10-4M; and 0.2M, respectively. However, Ammonium Acetate was incorporated into the deposition bath with concentrations that were varied from 3.0 mM to 12.2 mM. Meanwhile, for comparison purposes associated to the initial physical and chemical properties of the CdS films; reference CdS films were deposited under the same above chemical bath conditions, but in the absence of Ammonium Acetate. The pH of the chemical bath was measured during the deposition process. The films’ morphology and the chemical composition were examined by Field Emission Scanning Electron Microscopy (FE-SEM), and the Energy Dispersive spectrometer (EDS), respectively. The X-Ray Diffraction (XRD) T/2T technique was applied to study the structure of the films, including the lattice parameters. Atomic Force Microscopy (AFM) was used to examine the films topography and to determine the root-mean-square (RMS) surface roughness of the films as well as the grain size. Dektak Surface Profilometer was used to determine the CdS films’ thickness, where the films’ optical properties were measured using UV-Vis-NIR spectrometer. Optical energy band gap (Eg), and absorption coefficient (α) were calculated from the transmission spectral data. INTRODUCTION Cadmium Sulfide (CdS) thin films play an important role in the development of cost effective and reliable photovoltaic devices. CdS thin films have been used as a junction partners in CdTe and CIGS based solar cells for many years. In addition to its suitable direct band gap, high absorption coefficient and low resistivity [1-4]; CdS buffer layer provides full coverage of an epitaxial layer for the rough polycrystalline surface of the absorber layer. This results in improving the device photocurrent by enhancing the solar cell absorption spectra in the UV range and in the cell circuit voltage [5,6]. There are several techniques that are used for CdS thin film deposition as such chemical bath deposition (CBD) [7,8], vacuum evaporation [9], sputtering [10], electrodeposition [11], molecular beam epitaxy (MBE) [12,13], screen printing [14], metal organic chemical vapor deposition (MOCVD) [15,16],
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