Modeling of an equivalent circuit for dye-sensitized solar cells: improvement of efficiency of dye-sensitized solar cells by reducing internal resistance

Internal resistance in dye-sensitized nanocrystalline TiO2 solar cells (DSCs) was investigated using electrochemical impedance spectroscopy measurements. Four resistance elements were observed in the impedance spectra. These resistance elements could be explained by variations of cell parameters and the dependence of resistance elements on the applied bias voltage. It is found that the resistance element related to charge transport at the TiO2/dye/electrolyte interface displays behavior like that of a diode, and the series resistance elements largely correspond to the sum of the other resistance elements. To minimize the internal resistance in DSCs, the influence of cell parameters such as sheet resistance of TCO glass substrate, roughness factor of platinum counter electrode and cell thickness, on the impedance spectra were studied. An equivalent circuit for DSCs is proposed based on these results. The combined efforts have led to fabricate an efficient DSC sensitized with black dye. A short circuit photocurrent density of 20.1 mA/cm(2), an open-circuit voltage of 0.71 V, a fill factor of 0.71 and an overall conversion efficiency of 10.1% was obtained when measured under standard AM 1.5 sunlight.