Dye-sensitized solar cells (DSSCs), assembling with nano-crystalline TiO2 adsorbed cis-Ru(dcb)(2)(NCS)(2) dye (known as N3) using polar solvent-treated poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) coating on a conductive glass (fluorine-doped tin oxide, FTO) as a counter electrode, were studied. The conductivity of a bare PEDOT:PSS film was only 2 +/- 0.05 S/cm. However, the conductivities of PEDOT:PSS films treated with dimethyl sulfoxide (DMSO), NN-dimethyl acetamide (DMAc), N,Ndimethyl formamide (DMF), and dichloromethane (DMC) reached 85 +/- 15, 45 +/- 10, 36 7, and 20 6S/cm, respectively. In addition, carbon blacks (0.02, 0.1, 0.5, 1.0, 2.0wt% with respect to PEDOT:PSS aqueous solution) were added into the DMSO-treated PEDOT:PSS solution (denoted as DMSO-PEDOT:PSS) to enhance the conductivity. Atomic force microscopy (AFM) images of PEDOT:PSS and various DMSO-PEDOT:PSS films coated on the FTO glasses were examined. The topographical images reveal that the increased surface roughness is responsible for the enhanced electrochemical property of the DMSO-PEDOT:PSS films. AC impedance technique was also employed to analyze the kinetics at the electrolyte/counter electrode interface. The DSSC using carbon black (0.1 wt%)-modified DMSO-PEDOT:PSS conductive coating as a counter electrode reached a cell efficiency of 5.81 % under 100 mW/cm(2). This efficiency is higher than a DSSC using Pt as a counter electrode (5.66%). (c) 2007 Elsevier B.V. All rights reserved.