It´s normally atributed to photoelectrochemistry but most of the examples are with semiconductors, where the required photon energy is smaller than a metal. Also when a electrode potential is applied it will decrease the required energy for the generation of photocurrents.
My setup doesn´t have any additional electrode potential. My electrodes are submerged in electrolyte (100mM NaCl) and are illuminated perpendicularly to the surface (625nm @ 6mW/mm^2).
I´m not using semiconductor electrodes so there shouldn´t be current in non UV wavelengths. I´m using different MEA (Au, TiN) but I´m still observing this current once the electrodes are illluminated, also if I illuminate just the tracks I see a voltage.
In the following article[Article Dawn of the evolution of photoelectrochemistry
] they explain the required energy if the difference between the Work function of the metal and the solvation energy of the electrons. The problem is that they don´t give any proof for this hypothesis.
Hi David,
It's the photovoltaic effect, or the Becquerel effect (not the photoelectric effect). The photoelectric effect depends upon applied electrode voltage, the photovoltaic/Becquerel effect does not. I'm told there can also be an impact of the photoconductive effect, where light makes a material more conductive, which can also creates a voltage difference.
Anyway, the point is, it the effect occurs across the visible spectrum and down into the near IR.
It is a very common problem in optogenetic experiments. If you do a search you'll see lots of papers discussing it (e.g. Kozaia and Vazquez., 2015) . Theoretically, there are certain coatings that can be applied to electrodes (e.g. ITO) that will prevent the effect, but I don't think many people go to that extent.
If you're using MEA, you're actually quite lucky, as your light induced artifacts should be very reproducible from day to day, hence you can generate a recording of them with no cells on the array to generate a pure artifact, and then simply subtract this signal from your data.
Thanks for the reply William,
In the paper you sent me they explain the generation of photocurrents with low energy photons or wide band gap due to multiphoton absorption, where basically two photon act as one and have double the photon energy.
The problem is for Two-photon absorption requires high power lasers (>10MW) or femtosecond lasers.[http://iopscience.iop.org/article/10.1088/0022-3719/9/1/006/pdf] Which is far away from the intensities I used (6mW/mm2).
I´m looking for other reasons for this sub-band gap photocurrent generation.
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