Abstract
Nanostructured ZnO thin films doped with cobalt from 5% to 20% were grown on glass substrates by a low-temperature chemical bath deposition (CBD) technique. We compared the doping efficiency of incorporating cobalt in ZnO nanostructured samples doped with cobalt via cobalt nitrate and cobalt chloride. The concentration of cobalt incorporated into the ZnO matrix was precisely determined using inductively coupled plasma mass spectroscopy (ICP-MS). Scanning electron microscopy (SEM) images showed that only at a 0.1 M ratio of the precursor solutions in CBD using cobalt nitrate as a dopant, the morphology of ZnO yielded hexagonally shaped nanorods. At a 1 M ratio of the precursor solutions, SEM images showed that the morphology of ZnO was nanoplatelets at all doping levels, irrespective of the doping method used. The synthesized nanostructures retained the wurtzite hexagonal structure only at 0.1 M precursor solution using cobalt nitrate doping, which was confirmed by X-ray diffraction (XRD) studies. In cobalt-doped samples using cobalt chloride as a dopant, XRD analysis confirmed the formation of a Simonkolleite structure. At 300°C, the Simonkolleite structure was converted to a wurtzite structure without changing the morphology. Electrical conductivity measurements at 300 K showed that ZnO nanorods doped with cobalt using cobalt nitrate yielded the lowest resistivity. The molarity of the precursor solution and dopant was found to have a substantial impact on the morphology and doping efficiency of the ZnO nanostructures.
Highlights
Transparent semiconductors made of conductive oxides can provide antireflection coatings to facilitate higher absorption in solar cells
We report the dependence of doping on morphology, optical property, absorption, electrical conductivity, and photoluminescence (PL) of Zinc oxide (ZnO) nanostructures doped with cobalt ranging from 5% to 20% grown on glass substrates
To fabricate ZnO nanostructures doped with cobalt, either cobalt chloride or cobalt nitrate with different Co/Zn molar ratios was added to the chemical bath precursor solution
Summary
Transparent semiconductors made of conductive oxides can provide antireflection coatings to facilitate higher absorption in solar cells. Various nanostructured materials are studied for controlling light to increase absorption in photovoltaic (PV) cells. Zinc oxide has a wide range of useful optical and electronic properties which make it a promising material for optoelectronic devices. Recent studies show that optical, magnetic, and electrical properties of ZnO nanostructures can be controlled by defect centers and defect densities present in the ZnO lattice [1, 2]. Cobalt is a promising material for doping ZnO due to its similar ionic radius, abundant electronic states, and the divalent state [1, 3]. Cobalt-doped ZnO thin films and nanostructures have been prepared by several deposition methods including sputtering, sol-gel, spin coating, solvothermal, ultrasonic spray, and pulsed laser deposition methods [5,6,7,8,9,10]
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