Photovoltaic performance and impedance spectroscopy of a purely organic dye and most common metallic dye based dye-sensitized solar cells

In this work, performances of an organic electron donor–π-bridge–electron acceptor (D–π–A) type RK1 dye and the most common metallic N719 dye based dye-sensitized solar cells (DSSCs) were compared. To gain insight into the behavior of these devices, current–voltage and impedance spectroscopic measurements were performed. From the current–voltage data, the parameters of cells including open-circuit voltage, short-circuit current, fill factor, solar energy-to-electricity conversion efficiency, series resistance, shunt resistance, and ideality factor were extracted. The RK1 based cell showed higher photovoltage, higher short-circuit current, solar energy-to-electricity conversion efficiency, higher shunt resistance and ideality factor. Using the Mott-Schottky plots, electrical properties of the cells were investigated and lower electron concentration was found for the RK1-DSSC. This high performance can be attributed to the higher absorption coefficient of the RK1 dye and relatively higher induced positive band-shift of the conduction band edge of the TiO₂ semiconductor. The trends of the recombination resistance and the chemical capacitance as observed in the measured impedance spectra have also confirmed high photovoltaic performance of the RK1 based cell. Impedance spectra of the devices were observed both voltage and frequency dependent. At low frequencies, significant contribution of trap states was observed.