On the Hysteresis of Current Density-Voltage Curves of Dye-sensitized Solar Cells

Abstract

Here, we report on the dependence of the current density-voltage (j-V) curves of dye-sensitized solar cells (DSSCs) on the condition of potential sweep - sweep direction and delay time. The phenomenon, termed as hysteresis, is ambiguously attributed to the capacitive nature of the mesoporous TiO2 photoelectrode or diffusional pseudo capacitance of the electrolyte solution in DSSCs. To explain the hysteresis, here, we have developed a simple model translating fundamental processes: generation, transport and accumulation of charges in a working DSSC. The numerical solution of the corresponding time-dependent j-V equation allowed us to calculate the j-V curves for different sweep directions and delay time. The model calculation suggests that the hysteresis originates at open circuit region due to double layer capacitance at the counter electrode and maximum power due to the chemical capacitance of the TiO2 film. Moreover, the double layer capacitance, at the exposed substrate/electrolyte interface, affects the j-V curves at short circuit region if the delay time is extremely short. All these capacitive elements are strongly related to the electrolyte; however, the mechanism needs to be explored further. (C) 2015 Elsevier Ltd. All rights reserved.