Texture and Bandgap Tuning of Phase Pure Cu2o Thin Films Grown By a Simple Potentiostatic Electrodeposition Technique

Abstract

Phase pure Cu2O is one of the most desirable p-type absorber materials for ZnO based all-oxide solar cell because of its reported direct bandgap(~2.17 eV) and a suitable band alignment with n-type ZnO electrodes. Highly textured phase pure Cu2O thin films have been grown by a simple electrodeposition technique with varying cathodic potentials (-0.3 to -1.0 V) using Fluorine-doped Tin Oxide (FTO) substrates as working electrodes and a carbon rod as a counter electrode immersed in an alkaline aqueous electrolyte held at ~60 0C for 40 min. The surface morphology, structural, optical properties of the as-deposited Cu2O thin films were characterized by Scanning Electron Microscopy (SEM), Surface profiler, X-ray diffraction (XRD), and UV-Vis-NIR Spectroscopy respectively. SEM micrographs revealed that the deposited thin films coherently carpet the underlying substrate and composed of sharp faceted well-define grains having size in the range of 0.5 – 1.0 µm . XRD analyses showed that all films are composed of polycrystalline cubic Cu2O phase only and have average crystalline domain size in the range 30 – 73 nm. The preferred crystalline orientation of phase pure Cu2O films were found to be changing from (200) to (111) with increasing cathodic potentials and showed highest (111) and (200) crystalline texture coefficient while grown at -1.0 and -0.8 V respectively. The estimated optical bandgap of the as-grown samples were found in the range (2.00 – 2.20) eV consistent with the previously reported results and the variation of the optical bandgap could be attributed to the variation of the film thickness. The performance of copper oxide films was tested by estimating LED ‘ON/OFF’ modulated surface photovoltage into a photoelectrochemical cell at zero bias voltage and was found to be reasonable to integrate them into optoelectronic devices.