Valence Band-Edge Engineering of Nickel Oxide Nanoparticles via Cobalt Doping for Application in p‑Type Dye-Sensitized Solar Cells

• Published in: ACS applied materials & interfaces 2012-11, Vol.4 (11), p.5922-5929
• Main Authors: Natu, Gayatri, Hasin, Panitat, Huang, Zhongjie, Ji, Zhiqiang, He, Mingfu, Wu, Yiying
• Format: Article
• Language: English
• Subjects: Cobalt - chemistry; Crystallization - methods; Electric Power Supplies; Electrodes; Equipment Design; Equipment Failure Analysis; Macromolecular Substances - chemistry; Materials Testing; Metal Nanoparticles - chemistry; Metal Nanoparticles - ultrastructure; Molecular Conformation; Nanotechnology - instrumentation; Nanotechnology - methods; Nickel - chemistry; Particle Size; Semiconductors; Solar Energy; Surface Properties
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/am301565j

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 Co x Ni1–x O y (0 ≤ x ≤ 0.1) were fabricated using sol–gel method. X-ray photoelectron spectroscopy revealed a surface enrichment of divalent cobalt ions in the Co x Ni 1‑x O y 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 (N A ) and apparent flat-band potentials (E fb). Both N A and E fb 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 Co x Ni1–x O y films increased with increasing amount of cobalt, as expected from the trend in the E fb. Co-doping increased both carrier lifetimes within the p-DSCs and the carrier transport times within the nanoparticulate semiconductor network. The nominal composition of Co0.06Ni0.94O y was found to be optimal for use in p-DSCs.