Measurement and analysis of the series resistance in a dye-sensitized solar cell

Measurement and analysis were performed on the series resistance (R) in a dye-sensitized solar cell which was composed of a photoelectrode, a I-3(-)/I- redox electrolyte, and a Pt-coated counter electrode. The photoelectrode was a porous TiO2 film which was formed on a fluorine-doped SnO2 (FTO) substrate and sensitized by a ruthenium dye. R-s was determined from current-voltage curves measured at different light intensities. R-s was about 40 Omega and almost independent of the illumination area. Measurement of the conductivity of electrolyte solution showed that the effect of solution resistance was small. The sheet resistance of the FTO substrate was measured after heat-treatment at different temperatures (350-550degreesC) with and without formation of TiO2 thereon. The sheet resistance increased by heat treatment at temperatures above 400degreesC. Digital simulation of potential and current distributions in the transparent electrode indicated that the resistance due to the FTO substrate was 14.3 Omega. Such resistance must have occurred also at the counter electrode. Geometry and arrangement of current collectors are very important to minimize the potential drop in the conducting substrate.