Fabrication of p-type semiconducting NiCo₂O₄ thin films using hydroxide nanoplatelet precursors and their application to N749-sensitized photocathodes

Abstract

NiCo₂O₄ is promising as one of the p-type oxide semiconductors for practical applications in optoelectronic devices. In this study, we have elaborated NiCo₂O₄ hexagonal nanoplatelet films and examined their photovoltaic properties. The film fabrication was actually achieved by four steps: the synthesis of hexagonal nanoplatelets of a Ni_1/3Co_2/3(OH)₂ precursor, the dispersion of the nanoplatelets in liquid media, the self-assembly of the nanoplatelets on dipped substrates, and the topological conversion of the hydroxide to the oxide by the heat treatment. The resultant NiCo₂O₄ thin films had structural features such as the crystallographic (111) orientation, the high specific surface area, and the high light-scattering ability. As a result, the NiCo₂O₄ thin films loaded with an N749 dye could work effectively as photocathodes in the configuration of dye-sensitized solar cells.