Studies on bandgap tuning of visible light active heterojunction CuO/ZnO nanocomposites for DSSC application

Hetero-junction CuO/ZnO nanocomposites have been synthesized by simple solution based two-step method in the weight ratios 1:3, 1:2 and 1:1. The crystallite phases of the constituent nanomaterials are confirmed by X-ray diffraction. Increase of CuO content shows significant changes in the absorption spectra with exciton and plasmon related bands of ZnO and CuO, respectively. The compositional analysis and surface chemical states have been probed using X-ray photo electron spectroscopy (XPS). The bandgap is found to decrease with the increase of CuO content. The hybrid system is found to be suitable for absorbing a wide region of incident light with its enhanced absorption characteristics. The synthesized composites show suppression of the broad green band emission from ZnO near to the plasmon band of CuO, enhancing the charge separation which can further minimize charge loss due to recombination. The shift and asymmetry related to Raman bands give a clear idea about the crystallinity and coupling between phonon and continuum level created by the CuO. This coupled system could serve as an efficient photoanode material for dye sensitized solar cells with enhanced efficiency. Among the three composites, 2:1 sample exhibits maximum efficiency.