Intensity Modulated Photocurrent/Photovoltage Spectroscopy is a method of finding out the following sample properties:
- minority carriers lifetime (recombination time),
- carrier transport time through a sample,
- diffusion constant,
- diffusion length (if sample thickness is known)
- sample thickness (if sample diffusion length is known)
- rate of charge transfers through interfaces
- and many more kinetic quantities
The IMPS/IMVS instrument is complementary to devices performing static photocurrent/photovoltage measurements like photoelectric spectrometers or a mini photoelectric spectrometer.
The instrument consists of:
- LED revolver light source
- Potentiostat for photocurrent and open circuit potential (OCP) measurement
- Sample Chamber that shields the sample from an external EM fields as well as from ambient light
- Electrochemical Cuvette with Pt and Ag/AgCl electrodes
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- Modulation frequency range: 1 µHz ÷ 10 kHz
- Number of LED wavelengths: 10
- Current ranges: from 10 mA to 1 pA
- Potential ranges: from -5 V to 5 V
The IMPS/IMVS software is very intuitive and does not require any additional training.
The measurement results shown below are obtained for nanocrystaline anatase on ITO foil in KNO3 electrolyte.
Nyquist (or Argand) plot showing real and imaginary part of photocurrent measured for range of light modulation frequencies.
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Nyquist (Argand) plot in 3d showing real and imaginary part of photocurrent as a function of light modulation frequencies.
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Bode plot showing photocurrent amplitude and phase shift with respect to light modulation. The apparent phase jump is due to the assumed phase range from -π to π.
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Real (X) and imaginary (Y) part of photocurrent as a function of light modulation frequency.
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Photocurrent in time. Warning: the current sign convention assumed is normal in contrast to potentiostatic measurements (adopted by all the potentiostats in the world) where IUPAC (inverse sign) convention is used.
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The measurements were performed and shared by prof. J. Kuncewicz (Jagiellonian University).