Comparative study of impedance spectroscopy and photovoltaic properties of metallic and natural dye based dye sensitized solar cells

Photoelectrical characterization and impedance spectroscopy are performed for Dye sensitized solar cells (DSSC) fabricated by using natural dye (Pomegranate extract) and metallic dye (N719). Dyes are characterized by ultraviolet–visible spectroscopy to study optical properties. Typical photovoltaic behaviors are observed with open circuit voltage of 0.52 and 0.7 V and short circuit current density of 0.34 and 14 mA/cm² for natural and metallic dyes based cells respectively. From current–voltage (I-V) measurements, fill factor, conversion efficiency and ideality factor are extracted. Electrical properties of the cells are investigated using Mott-Schottky plots. To gain insight into charge transport, voltage and frequency dependent impedance spectroscopy is performed. Photovoltaic performance of cells is evaluated from the trends of recombination resistance and chemical capacitance in the measured impedance spectra. Significant contribution of interface trap states is observed at low frequencies and reversal of the polarity of capacitance from positive to negative values is observed at higher frequencies. The overall behavior of devices is compared. To our knowledge these impedance spectroscopy results for natural dye based solar cell are not reported earlier. Their insight and understanding is important for optimizing various components and interfaces for the development of cost effective commercially available natural dyes based DSSCs.