Utilization of electrochemical impedance spectroscopy for experimental characterization of the diode features of charge recombination in a dye sensitized solar cell

• The diode-like behavior of charge recombination in a DSSC is investigated.
• The experimental considerations for detailed EIS studies of DSSCs are examined.
• The bias dependent series resistance and the diode junction voltage are determined.
• The DSSC diode ideality factor is measured using D.C. and A.C. techniques.
• Component resolved impedance spectroscopy probes the interfaces within the DSSC.

The anode-electrolyte interface is a primary location for charge recombination in a dye sensitized solar cell (DSSC), and hence acts as a major efficiency-limiting factor of the device. The electrical signature of this recombination effect is similar to that of a semiconductor diode, and at the same time serves as an indicator of the recombination mechanisms. The present work focuses on certain detailed aspects of the experimental detection and analysis of this diode-like behavior of a DSSC. The recombination process is activated in a forward biased dark cell containing a photo-anode of multilayered TiO2 particles. The resulting reaction kinetics are probed with a combination of D.C. voltammetry and strategically designed electrochemical impedance spectroscopy (EIS). The voltage dependent impedance parameters of the multi-component solar cell are obtained from complex nonlinear least square analysis of the EIS data. Among these parameters, the characteristic frequency and the recombination resistance of charge transfer at the TiO2-electrolyte interface follow the same diode-like voltage dependence as that of the cell's D.C. current. The experimental considerations for analyzing these effects in a quantitative approach are discussed. The ideality factor of the DSSC diode is dictated by charge recombination in the mesoporous TiO2 photo-anode, and emerges with mutually agreeing values from independent D.C. and A.C. measurements. The results illustrate how the component-resolved analytical capability of EIS can be utilized for a detailed evaluation of the electrochemical performance of a DSSC.