Electrochemical properties of carbon black (CB) porous layer as a counter electrode in dye-sensitized solar cells (DSC) are studied. CB electrode for triiodide (I-3(-)) ion reduction is coated with spray coating method on the fluorine-doped tin oxide glass at 120 degrees C. The CB particle size is varied from 20 nm to 90 nm and the CB electrode thickness is controlled from 1 mu m to 9 mu m by controlling the spraying time. The electrochemical impedance spectroscopy is analyzed for a symmetric cell and a new circuit model is applied to identify electrochemical parameters. As the CB particle size is decreased, the catalytic activity is improved because of the increase in the surface area and the conductivity of the CB layer. Increased CB electrode thickness also improves the catalytic activity and leads to the low charge transfer resistance at the electrolyte/CB electrode interface. The CB counter electrode with the particle size of 20 nm and the thickness of 9 mu m for DSC shows the energy conversion efficiency of 7.2% with the highest fill factor (FF) of 65.6%. which is similar to the Pt counter electrode with FF of 65.8% and the efficiency of 7.6%. (C) 2012 Elsevier Ltd. All rights reserved.