Improvement of efficiency of dye-sensitized solar cells based on analysis of equivalent circuit

The present paper discusses the principle of dye-sensitized solar cells (DSCs) in terms of a new physics-based equivalent circuit model. This model is proposed following analysis by electrochemical impedance spectroscopy of the voltage dependence of the internal resistance elements of DSCs. The influence of these elements upon cell performance in areas such as short circuit current density (JSC), open circuit voltage (VOC) and fill factor (FF) was examined based on the equivalent circuit. It was demonstrated that the haze factor of TiO2 electrodes is a useful index when fabricating light-confined TiO2 electrodes to improve JSC, and that blocking the TiO2 surface with molecules is an effective way of reducing interfacial charge recombination at the TiO2 surface and of improving shunt resistance and VOC. FF was also improved by reduction of the internal series resistance, which is composed of the following three elements: the redox reaction resistance at the platinum counter electrode, the resistance of carrier transport by ions in the electrolyte, and resistance due to the sheet resistance of the transparent conducting oxide. Finally, the highest efficiency scores of 10.4% and 10.8% (aperture illumination area 1.004 cm2 and 0.2227 cm2, respectively) were confirmed by a public test center.