Abstract:
Thin films are nanoscale materials which are widely used for solar cells and other
optoelectronic devices. Cd(1-x)ZnxS (cadmium zinc sulphide) is formed by incorporating zinc
ions to CdS (cadmium sulphide). Cd(1-x)ZnxS is a n-type semiconductor material which has a
wider band gap than that of n-type CdS. Therefore, Cd(1-x)ZnxS can be used as a window
material when application required low absorption of light and n-type semiconductor
properties. Cd(1-x)ZnxS has been electro-deposited by varying cadmium ion concentration,
zinc ion concentration, pH, deposition temperature and deposition time. Results reported here
were based on the depositions conditions; 0.1 mol dm-3 cadmium ion concentration, 0.01 mol
dm-3 zinc concentration, 2.45 - 2.50 pH and 50 °C deposition temperature. Electro-deposition
experiments were carried out by Gamry ―series G 300‖ potentiostat while, working electrode
was fluorine doped tin oxide/glass substrate, reference electrode was Ag/AgCl electrode and
counter electrode was a semi-spherical graphite rod. The deposition voltage was identified
from the cyclic voltammograms and shapes of the deposition current vs time plots. Electrodeposition
reported in here was carried out at under-deposition voltages. The best values for
electro-deposition parameters; voltage, pH, temperature and time were identified by
observing their influence on the band gap values of the thin films deposited and the open
circuit voltages of photo-electrochemical cell consisting of 0.1 mol dm-3 sodium thiosulphate
electrolyte and the thin film semiconductor. A band gap range of 2.5 eV – 2.6 eV was
obtained for Cd(1-x)ZnxS layer which is higher than the band gap of CdS. The open circuit
voltage varied from -48 mV to -190 mV during optimization of voltage, pH, temperature and
time. An X-ray diffraction spectrum has shown that Cd(1-x)ZnxS layer has a single hexagonal
crystal phase. The crystal parameter, a = 4.1264 Å and it was lower than the standard CdS (a
= 4.1364 Å). The results indicate that Cd(1-x)ZnxS thin films can be produced under the given
conditions as a window layer for thin film solar cells in order to harvest more light and hence
to improve the efficiency.
