Impedance measurement of Cobalt doped ZnO Quantum dots.

We investigated structural, thermal and electrical properties of ZnO Quantum dots grown by precipitation method. QDs were spin coated on ITO and annealed at various temperatures ranging from 100$^{\mathrm{0}}$C to 300 $^{\mathrm{0}}$C. ZnO QDs were doped with cobalt for concentration ranging from 0-15{\%}. XRD measurement showed increase in bond length, strain, dislocation density and Cell volume as the doping level varied from 0{\%} to 15{\%}. Impedance Spectroscopy measurements represented by Cole-Cole plot showed reduction in resistance as the cobalt doping concentration increased from 0-15{\%}. Thermal activation energy was obtained by plotting resistivity Vs temperature for doped samples at temperatures from 100$^{\mathrm{0}}$C to 300$^{\mathrm{0}}$C. The thermal activation energy decreased from 85.13meV to 58.21meV as doping increased from 0-15{\%}. Relaxation time was extracted by fitting data to RC model. Relaxation time varied from 61.57 ns to 3.76 ns as the cobalt concentration increased from 0{\%} to 15{\%}. We will also discuss applications of cobalt doped ZnO QDs on improving conversion efficiency of solar cells.