CdTe Deposition and Characterisation

Abstract

The main absorber material used in solar cells described in this book is CdTe. This chapter provides an insight to the electrodeposition of cadmium telluride (CdTe) layers. CdTe thin films were electrodeposited on glass/fluorine-doped tin oxide (FTO) using a two-electrode system from an acidic and aqueous solution containing 1.5 M Cd(NO3)2·4H2O and 0.002 M TeO2 at pH = 2.00 ± 0.02. The grown layers were characterised for their structural, optical, morphological, compositional and electronic properties using X-ray diffraction (XRD) and Raman spectroscopy, UV-visible spectrophotometry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), photoelectrochemical (PEC) cell and DC conductivity measurements, respectively. The XRD study reveals that the ED-CdTe layers are polycrystalline in nature with preferential peak orientation along the (111) plane. The highest crystallinity was observed when grown at 1370 mV cathodic potential with reference to graphite electrode. Optical absorption reveals that the bandgap of the as-deposited, heat-treated and CdCl2-treated CdTe layers falls within the range 1.48–1.50 eV. The SEM micrographs show a uniform coverage of the underlying glass/FTO substrate. The EDX shows the effect of growth voltage on the atomic composition of CdTe layers with 1:1 atomic ratio of the deposited CdTe layers grown at 1370 mV. The PEC cell measurements reveal that both p- and n-type CdTe layers can be electroplated. The effect of F, Cl, I and Ga as dopants to CdTe baths was evaluated and documented.