Dye-sensitized solar cells (DSSCs) have received much interest as possible future low cost solar cells
as DSSCs use inexpensive materials and simple processes. To improve cell performance for wide-scale
applications, understanding of parameter behaviors through equivalent circuit modeling are important,especially dynamic behavior. DSSC dynamic parameters can be determined by using impedance
spectroscopy through a variety of characterization methods. In previous works [1-4], impedance
characteristics of c-Si and a-Si solar cells have been presented and analyzed. In this paper, we derive the
dynamic impedance of a DSSC under dark using a FRA. Voltage and frequency dependences of DSSC
dynamic parameters are shown.
In general, a DSSC is composed of a transparent conducting oxide (TCO) glass covered with metal
oxide (i.e.TiO2), dye molecules attached to the surface of metal oxide, a redox couple electrolyte, and a
catalyst (i.e., platinum) coated on transparent conducting glass as a counter electrode. Under illumination
the AC or dynamic equivalent circuit of a DSSC when connecting to a load can be represented as Fig.
1(a) [5-6]. Resistance 1 (R1) and capacitance 1 (C1) are elements of impedance 1 (Z1) due to redox
reaction at the platinum counter electrode. Z2 represents as a diode, taking into account electron transfer
at the TiO2/dye/electrolyte interfaces. R3 and C3 are elements of Z3 relating to carrier transport of ions
within the electrolyte. Shunt resistance (Rsh) accounts for back electron transfer across the
TiO2/dye/electrolyte junctions. Sheet resistance (Rs) accounts for the transport resistance of TCO
substrate.