Synthesis and Characterisation of CdTe Thin Films
Mohammad Lamido Madugu, Olajide Ibukun-Olu Olusola, Abdullahi Lawal
Keywords: CdTe, electroplating, CdCl2-treatment, PEC cell
The present global energy, largely from the conventional sources can be depleted in the near future, hence the need for a sustainable alternative sources energy for the growing world population. Photovoltaic (PV), a renewable energy source has been identified as the best alternative source for a sustainable energy due to it cheap, simplicity and environment friendly nature. The PV solar cell devices were usually made from materials with specific properties called semiconductors. One of such semiconductor material is cadmium telluride (CdTe), which is used as an absorber layer in CdS/CdTe solar cell. Cadmium telluride (CdTe) thin films have been synthesised using a simple and cost-effective 3 – electrode electroplating technique. The deposition was carried out from aqueous acidic electrolyte composed of laboratory grade reagent CdSO4 and TeO2. The films were deposited on a cathode made from glass/fluorine doped tin oxide (glass/FTO) substrate. A saturated calomel electrode (SCE) was used as the reference with respect to platinum (Pt) anode. The pH and temperature of the bath were 2.00±0.02 and |80OC respectively. This indicates that the films were deposited in an acidic medium. After deposition, each sample was divided into two, one left as-deposited and the other annealed in the presence of CdCl2. Thereafter, the films were characterised for their structural, morphological and optical properties. The structural properties studied using x-ray diffraction (XRD) showed that the material is crystalline in nature with preferred orientation along the (111) and (211) cubic phases of CdTe. The surface morphology of the films showed that the CdTe material is crystalline with visible grains agglomeration. Increase in grain size with increase in annealing temperature was observed from the films morphology. Optical studies revealed that the bandgap for both as-deposited and the annealed materials show a similar bandgaps of 1.50 eV. Photoelectrochemical (PEC) cell studies were conducted to find the electrical conduction type of the layers in both as-deposited and annealed conditions. The study showed that the material is p-type at the lower voltages (V < 828 mV) and n-type at higher voltages (V > 828 mV). After CdCl2 treatment, all layers transformed to p-type. The successful deposition and characterisation of CdTe thin films have been carried out and the results from the various characterisation techniques show that the materials will be suitable for solar cell development.