Wet-electrochemical growth of CdTe layers for photovoltaic applications

Cadmium telluride (CdTe) thin films have been prepared using a low-cost potentiostatic electrochemical technique from an aqueous electrolyte. A standard three-electrode geometry was employed for the deposition of the samples. The possible growth potentials for the electrodeposition of CdTe were optimized using cyclic voltammetry. The samples were grown at potentials - 0.5, - 0.6, and- 0.7 V with respect to Ag/AgCl reference electrode and annealed at 450 degrees C for 20 min. The optical, structural, morphological, compositional, and electrical properties were studied with a range of analytical techniques. The as-prepared samples exhibited amorphous behavior and the polycrystalline nature with cubic crystal structure was revealed after annealing. The annealed sample grown at -0.7 V exhibits pure CdTe reflections without the TeO2 phase. The Raman analysis confirms the reduction in the A1 mode of Te systematically with increasing the growth potential and vanishes completely for the sample grown at - 0.7 V. Uniform, densely packed, and spherical surface morphology with stoichiometric CdTe (Cd:Te composition ratio 1:1) layers were obtained at - 0.7 V. The Te-Cd and Te-O bonds were revealed in XPS core-level spectra; however, the increased peak intensity ratio of Te 3d(5/2) and Te 3d(3/2) confirms the reduction of the TeO2 phase in CdTe. The increased carrier concentration and flat band potential calculated for the sample grown at - 0.7 V demonstrate the growth of low-defective and highly crystalline CdTe layers.