We demonstrate herein the self-assembly of CoS nanosheets into CoS nanoflowers in the reaction solution and ordered nanosheets arrays on the conductive substrate through a citrate-ligand-assisted hydrothermal reaction. The CoS nanosheets arrays exhibit more active sites, faster electronic transmission channels, and better electrocatalytic activity for the reduction of I-3(-) than the CoS nanoflowers due to the unique structure of the former. The dye-sensitized solar cell with the CoS nanosheets arrays yields power conversion efficiency of 9.50%, which is higher than that based on the CoS nanoflowers (7.66%) and that based on the Pt control cathode (8.58%). In addition, the CoS nanosheets arrays based quasi-solid-state dye-sensitized solar cell with an iodine gel electrolyte exhibits excellent long-term stability under one-sun soaking. This finding indicates that the CoS nanosheets arrays are the promising replacement of Pt as the low-cost and high-efficiency counter electrode material in dye-sensitized solar cells. (C) 2019 Elsevier Ltd. All rights reserved.