I am using FTO glass for DSSC fabrication. I have two questions related to the resistivity of FTO glass:
1) We ordered FRO glass with 10 ohm resistivity, but when I check, it is around 30 ohm. Also, I notice that resistivity changed by changing the distance between the two multimeter probes, so how can I know the right resistivity of the glass?
2) I need to reuse the FTO glass; therefore, I dipped the glass in acetone and soap for 1 day, then I cleaned it by sonication in acetone, methanol and water for 30 min in each. Then I measured the resistivity, and now it is around 50 ohms, and also it is affected by the distance between the probes. How can I know the value of the resistivity that confirms that the FTO cannot be used anymore?
Hello Zainab
I can't help you with 2) but regarding the first part of your question you are mixing sheet resistance (given by the FTO manufacturer as 10Ω/□ (ohms per square)) with resistance. Sheet resistance is the 2D equivalent of the bulk resistivity and is essentially resistivity divided by film thickness. As such it is a material property and hence the actual resistance (in Ohm) depends on the probe distance while the sheet resistance (in Ohm/square) is a material property. With a simple 2 wire multimeter you can not directly measure sheet resistance. For that you need a 4 point probe either in Van der Pauw or linear geometry which a) removes your contact and wire resistance and b) eliminates the probe distance out of the equation and there are known correction factors one can apply regarding the ratios of the overall sample size and thickness with the probe distance.
There is a good description how to get sheet resistance from 4pp measurements here: https://www.ossila.com/pages/sheet-resistance-theory
If you don't have a 4pp system you can try to use the multimeter by reducing the probe distance to give you the numerical equivalent of the sheet resistance and then always stick to that distance. However this is a crude way to do it as i.e. residue from contamination can change the probes contact resistance and hence change the reading.
Hope this helps
Karsten
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