Structural, optical, electrical and morphological properties of CdS films deposited by CBD varying the complexing agent concentration

Abstract

CdS thin films were deposited on commercial glass substrates by CBD technique at constant temperature and deposition time of 90 °C and 50 min, respectively. The reaction was performed by mixing cadmium acetate, ammonium acetate, ammonium hydroxide, thiourea, and deionized water as an aqueous medium. The S/Cd ratio in the solution was kept constant at 4.46 to make sure that the films were as stoichiometric as possible. Optical, electrical, structural properties and the presence of organic compounds in the films were studied modifying the concentration of ammonium hydroxide (complexing agent) in the bath solution. X-ray diffraction patterns show that all films have the cubic phase with a preferential orientation in the plane (1 1 1). An increase of the film’s resistivity from 102 to 107 Ω-cm is observed by increasing the ammonium hydroxide concentration in the solution in the narrow interval of 0.18–0.36 M. Transmittance values up to 70% are obtained at the lowest concentrations of this reagent, obtaining from these spectra the highest value of the direct bandgap, 2.37 eV. Results about the presence of organic compounds and their influence on the photoluminescence properties are shown, which have not been reported to date. The main organic compound identified by FTIR is cyanamide, whose concentration is higher at the lowest ammonium hydroxide concentrations. Photoluminescence spectra of the films show green, red and orange bands, located at 2.27 eV, 1.78 eV, and 2.02 eV, respectively. An additional band was observed with low intensity at 2.99 eV associated with the presence of nanoparticles in some films. The films with the lower presence of defects, higher uniformity and best optical, electrical and structural properties for their use as window material in solar cells are those deposited from a bath solution with a 0.24 M concentration of the complexing agent. Keywords: CdS films, CBD, Low resistivity, High transmission, Organic compounds, Radiative transitions