Morphology and Optical Properties of Template Synthesized Copper-Telluride Nanowires

Abstract

Copper tellurides (CuxTe) are important class of materials suitable for use as active components in CdTe based solar cells. Among all these wide band gap materials, copper telluride is a very important material for wide range of applications. Copper tellurides (CuxTe) have different crystal structures depending upon the value of x (1<x<2) and are usually p-type compound semiconductors. Copper tellurides (CuxTe) are widely used as back-contact materials to CdS/CdTe photovoltaic devices for higher efficiency and stability of the device.Cu2Te/n-CdTe hetero-junction solar cells have been reported with an efficiency reaching 7.5%. We report here the morphological and optical properties of template synthesized copper-telluride nanowires. The copper tellurides (CuxTe) nanowires were synthesized on copper and ITO-coated glass (with ITO thickness of 1500A and resistivity of 15-20 Ohm-cm) substrates via template-assisted (polycarbonate tracketch membrane) electrodeposition technique at room temperature (303K). The morphologies of copper telluride nanowires were studied by scanning electron microscopy which reveals the uniform growth of standing nanowires of identical diameter equal to the diameter of the template used. The electrodeposited nanowires are found to be highly ordered, vertically aligned and of high aspect ratio. To investigate the optical properties of as-synthesized copper telluride nanowires, we performed UV-Vis measurements at room temperature (303K). It is found from the absorption spectra that the optical absorption edge moves to shorter wavelength region with decrease in diameter. The band gap energy is found to be 2.78, 3.10 and 3.37eV for 200, 100 and 50nm copper telluride nanowires, respectively. The change in the band gap with diameter shows the “blue shift” in copper telluride nanowires which can be attributed to the quantum size effect in nanowires. We found broad PL emission spectra of 200, 100 and 50nm copper telluride nanowires and photoluminescence emission peak at around 456nm in the blue region (450-475nm) with excitation wavelength of 220nm were observed. The other emission peak at around 555nm is also observed in all copper telluride nanowires respectively which attributed to the green emission in the visible region.