Preparation of CoS2 nanoflake arrays through ion exchange reaction of Co(OH)2 and their application as counter electrodes for dye-sensitized solar cells

Abstract

The cobalt sulfide nanoflake arrays prepared by the transformation of Co(OH)₂ nanoflake arrays using the ion exchange reaction method were incorporated into Pt-free dye-sensitized solar cells (DSSCs). Morphologies and crystal structures of the cobalt sulfide and cobalt hydroxide nanoflakes arrays were characterized by SEM, TEM and XRD analyses. The electrochemical properties were determined by cyclic voltammetry (CV) measurement. The cobalt sulfide nanoflakes which were composed of CoS₂ single crystals and their aggregates dispersing in the amorphous cobalt sulfide matrix were completely transferred by substitution of S²⁻ for O²⁻ in the ion exchange reaction. The DSSC assembled with cobalt sulfide nanoflake arrays as the counter electrode showed a photovoltaic conversion efficiency of 5.20%, which was close to that of DSSC with sputtered Pt as the counter electrode (5.34%). Therefore, the cobalt sulfide nanoflake array film can be considered as a promising alternative counter electrode for use in DSSCs due to its large surface area and high electrocatalytic performance.