Morphology dependent photovoltaic performance of zinc oxide-cobalt oxide nanoparticle/nanorod composites synthesized by simple chemical co-precipitation method

Abstract

Zinc oxide-cobalt oxide nanocomposites (ZnO–Co3O4 NCs) with diverse concentrations (0.03, 0.06, 0.09 and 0.12 M) of Co2+ ions were synthesized by a simple chemical co-precipitation method. The effect of Co2+ ions concentration on the optical, structural, morphological and chemical properties of the ZnO–Co3O4 NCs was investigated by UV–Vis spectrophotometer, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDAX) spectroscopy, nitrogen adsorption-desorption and photoluminescence (PL) spectroscopy analysis. The presence of visible light responsive Co3O4 induced red shift in the absorption and reduced band gap energy of the ZnO–Co3O4 NCs. The XRD patterns confirmed the coexistence of hexagonal wurtzite structured ZnO and face-centered cubic structured Co3O4 in the ZnO–Co3O4 NCs. The FESEM images of the ZnO–Co3O4 NCs disclosed the formation of composite nanostructure morphology comprised of nanoparticles and nanorods. The nitrogen adsorption-desorption isotherms disclosed a relatively high specific surface area of ZnO(0.44)-Co3O4(0.06) NC with 8.97 m2/g when compared to the pure ZnO NPs (1.65 m2/g). The PL spectra revealed the least photogenerated electron–hole recombination rate and highest photogenerated electron lifetime in the ZnO–Co3O4 NCs over ZnO NPs. The dye-sensitized solar cells fabricated using the pure ZnO NPs and ZnO–Co3O4 NC photoanodes exhibited dissimilar photovoltaic performance due to the morphology dependent dye loading, light scattering and electron transport properties of the respective photoanodes.