In this study, a transparent counter electrode (CE) based on cobalt sulfide (CoS) nanosheet arrays (NSAs) was incorporated for the first time in dye-sensitized solar cells (DSCs). First, Co(OH)(2) NSAs were electrodeposited onto a fluorine-doped tin oxide glass substrate, and then conversed to CoS NSAs by soaking in a chemical bath. UV-vis spectrophotometry, cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization measurements indicate that the resultant CoS NSAs CE exhibited both high transmittance (>70%) at wavelength of 550 nm and superior electrocatalytic activity for I-3(-) reduction to a conventional Pt CE. The DSC assembled with the CoS NSAs CE displayed an impressive photovoltaic conversion efficiency of 6.39%, which even surpassed the DSC using a Pt CE (6.06%). (C) 2013 Elsevier Ltd. All rights reserved.