Description
Intensity-modulated photocurrent spectroscopy (IMPS) is a useful technique to gain valuable information about dye-sensitized solar cells (DSSCs) or other types of solar cells such as electron-transport time τtr, the charge collection efficiency ηcc, and the diffusion coefficient D. This experiment requires a bi-potentiostat setup. The first potentiostat (MASTER) controls the light source and modulates the intensity of the light beam focused onto the cell while the second potentiostat (SERF) controls the cell's potential and measures the photo-current.
IMPS and IMVS are related to electrochemical impedance spectroscopy (EIS). In EIS, a constant potential or current signal is applied to a cell which is superimposed by a sinusoidal AC signal which frequency is stepwise modulated. The measured sinusoidal signal has the same frequency as the applied signal but it is phase-shifted. The frequency-dependent impedance Z can be then calculated for each frequency, displayed in a so-called Bode plot.
Both IMPS and IMVS operate similarly. Instead of applying a current or potential signal to the cell, a light beam is focused on a DSSC with a base intensity IDC that is superimposed by a sinusoidal waveform with amplitude I0. The frequency f of the sine wave is step-wise changed during an experiment.
The angular frequency ω can be expressed as:
Similar to EIS the measured signal has the same frequency as the applied signal, but its phase is shifted. By analyzing the real and imaginary portion of the measured photo-current, time-dependent information about various processes such as diffusion coefficients or reaction rates can be obtained.
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Please see Gamry's Application Notes for more information about measurements on DSSCs: •Dye Solar Cells – Part 1: Basic principles and measurements |
