Valence Band-Edge Engineering of Nickel Oxide Nanoparticles via Cobalt Doping for Application in p-Type Dye-Sensitized Solar Cells
By Natu, Gayatri; Hasin, Panitat; Huang, Zhongjie; Ji, Zhiqiang; He, Mingfu & Wu, Yiying
Published in ACS Applied Materials & Interfaces
2012
Abstract
We have systematically studied the effects of substitutional doping of p-type nanoparticulate NiO with cobalt ions. Thin films of pure and Co-doped NiO nanoparticles with nominal compositions CoxNi1 -xOy (0 ≤ x ≤ 0.1) were fabricated using sol -gel method. X-ray photoelectron spectroscopy revealed a surface enrichment of divalent cobalt ions in the CoxNi1-xOy nanoparticles. Mott -Schottky analysis in aqueous solutions was used to determine the space charge capacitance values of the films against aqueous electrolytes, which yielded acceptor state densities (NA) and apparent flat-band potentials (Efb). Both NA and Efb values of the doped NiO were found to gradually increase with increasing amount of doping; thus the Fermi energy level of the charge carriers decreased with Co-doping. The photovoltage of p-DSCs constructed using the CoxNi1 -xOy films increased with increasing amount of cobalt, as expected from the trend in the Efb. Co-doping increased both carrier lifetimes within the p-DSCs and the carrier transport times within the nanoparticulate semiconductor network. The nominal composition of Co0.06Ni0.94Oy was found to be optimal for use in p-DSCs.