The Intensity-Modulated Photocurrent & Photovoltage Spectroscopy System allows to perform sample examination that is complementary to static photovoltage/photocurrent measurements. Monochromatic LED with modulated light intensity of sinusoidal waveform in wide range of frequencies enables to investigate many kinetic quantities: diffusion parameters, time scales of the sample: carrier transport time, recombination rates and many others. In case of photoelectrochemical samples immersed in an electrolyte, the sample may be illuminated on both sides: through the electrolyte, to investigate electrolyte-sample surface interface, or through the rear optical window for substrate-sample interface examination. The sample setup is placed in the Sample Chamber that screens ambient light and external EM fields.
Quantities measured by the instrument:
- Minority carriers lifetime (recombination time),
- Carrier transport time through the sample,
- Rate of the charge transfer through the interfaces,
- Diffusion constant,
- Diffusion length for a given sample thickness,
- Sample thickness for a given diffusion length,
- Other kinetic quantities.
The instrument consists of:
- LED Changer light source,
- Potentiostat for photocurrent and Open Circuit Potential (OCP) measurement,
- Electrochemical Shielding Box that screens the external EM fields as well as ambient light,
- Electrochemical Cuvette with Pt and Ag/AgCl electrodes.
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LED Changer
- 10 LED slots,
- Default LED set: 365 nm, 385 nm, 405 nm, 450 nm, 520 nm, 590 nm, 630 nm, 740 nm, 840 nm, white (3000 K),
- Custom LED selection available,
- Typical electric power of LEDs: 3W,
- Light intensity modulation: square, saw or sinusoidal waveform with adjustable amplitude and bias light intensity,
- Light modulation frequency range: 1 µHz ÷ 10 kHz,
Controller
- Maximum sampling rate: 1 kSample/s,
- Connection with PC: via USB 2.0,
Potentiostat
- Bias potential range: -5 V ÷ 5 V,
- Current ranges: 10 nA, 100 nA, 1 µA, 10 µA, 100 µA, 1 mA, 10 mA,
- Current resolution: from 1 pA to 100 nA (range dependent),
Electrochemical cuvette
- Adapted for transparent and opaque samples,
- PTFE container for electrolyte,
- Reference electrode: Ag/AgCl,
- Counter electrode: Pt.
The measurement results shown below are obtained for nanocrystaline anatase on ITO foil in KNO3 electrolyte.
Photocurrent spectrum.
Warning: the current sign convention assumed is normal in contrast to potentiostatic measurements (adopted by all the potentiostats in the world) where the IUPAC (inverse sign) convention is used.
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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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