Electrodeposition and characterisation of CdS thin films using thiourea precursor for application in solar cells

CdS thin films have been successfully electrodeposited on glass/FTO substrates using acidic and aqueous solution of CdCl2.xH2O and thiourea (SC(NH2)2). The electrodeposition of CdS thin films were carried out potentiostatically using a 2-electrode system. The prepared films were characterised using X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM), Atomic force microscopy (AFM), Photoelectrochemical (PEC) cell measurements, Electrical resistivity measurements and UV-Vis spectrophotometry to study their structural, compositional, morphological, electrical and optical properties, respectively. The structural studies show that the as-deposited and annealed CdS layers are polycrystalline with hexagonal crystal structure and preferentially oriented along (200) planes. The optical studies indicate that the ED-CdS layers have direct bandgaps in the range (2.53-2.58) eV for the as-deposited and (2.42-2.48) eV after annealing at 400oC for 20 minutes in air. The morphological studies show the good coverage of the FTO surface by the CdS grains. The average grain sizes for the as-deposited and annealed layers were in the range (60-225) nm. These grains or clusters are made out of smaller nano crystallites with the sizes in the range ~(11-33) nm. The electrical resistivity shows reduction as thickness increases. The resistivity values for the as-deposited and annealed layers were in the range (0.82-4.92)×105 Ωcm. The optimum growth voltage for the CdS thin films was found to be at the cathodic potential of 797 mV with respect to the graphite anode. No visible precipitations of elemental S or CdS particles were observed in the deposition electrolyte showing a stable bath using thiourea during the growth.