Investigation of electrodeposited cobalt sulphide counter electrodes and their application in next-generation dye sensitized solar cells featuring organic dyes and cobalt-based redox electrolytes

Cobalt sulphide (CoS) films are potentiodynamically deposited on fluorine-doped tin oxide (FTO) coated glass substrates employing one, three and five sweep cycles (CoS-I, CoS-III and CoS-V respectively). Analysis of the CoS-III film by impedance spectroscopy reveals a lower charge transfer resistance (R-CT) than that measured for Pt CE (0.75 Omega cm(-2) and 0.85 Omega cm(-2), respectively). The CoS films are used as counter electrodes (CE) in dye-sensitized solar cells (DSSCs) featuring the combination of a high absorption coefficient organic dye (C218) and the cobalt-based redox electrolyte Co(bpy)(3). DSSCs fabricated with the CoS-III CE yield the highest short-circuit current density (J(SC)) of 12.84 mA cm(-2), open circuit voltage (V-OC) of 805 mV and overall power conversion efficiency (PCE) of 6.72% under AM 1.5G illumination (100 mW cm(-2)). These values are comparable to the performance of an analogous cell fabricated with the Pt CE (PCE = 6.94%). Owing to relative lower cost (due to the inherit earth abundance of Co) and non-toxicity, CoS can be considered as a promising alternative to the more expensive Pt as a CE material for next-generation DSSCs that utilize organic dyes and cobalt-based redox electrolytes. (C) 2014 Elsevier B.V. All rights reserved.