I am using gold interdigitated electrodes with 5 um width and spacing. I spin coat PEDOT-PSS on the IDE to get around 100 nm thick films. In-situ conductance measurements are done by dipping the IDE in 0.1 M TBAP solution in acetonitrile and using Ag wire as reference and Pt foil as counter electrode. I am recording currents (I1 and I2) at two working electrode of IDE by varying potential (Vg) from -0.8 to +0.6 V keeping the Vd = 20mv. I am getting very high conductance (~0.2 S) on doping which is maintained from 0 to +0.6 V. Conductance in the de doped state is ~ 10-5 S. Is this high value of conductance is due to shot between the IDE electrodes? However, I have checked with multimeter and they have resistance more than Mega ohms. Is there any other way to find out whether the electrodes are shot or not?
I dont know much about the technique u mentioned here however, the following thesis will help a lot.
http://alexandria.tue.nl/extra2/200712256.pdf
http://repository.tue.nl/631615
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Hello!
There may actually be nothing wrong with Your results at all, but rather it is PEDOT-PSS that may be quite difficult to dedope overall. The PEDOT-PSS commercial product is a water coloidal dispersion of an oxidised poly(3,4-ethylenedioxythiophene) (polycation), charge counterbalanced with poly(styrene sulphonate) (polyanion). Dedoping this, rather peculiar polymer "blend", would thus require either the removal of the poly(styrene sulphonate) polyanion upon reduction of the oxidised poly(3,4-ethylenedioxythiophene) macromolecule, or uptake of a cation, to counterbalance the charge of the poly(styrene sulphonate) polyanion, once the poly(3,4-ethylenedioxythiophene) gets charge neutralised upon reduction. Your results may suggest that Your PEDOT-PSS films get only slightly dedoped, as the ingres of tetrabutylammonium cations may be ineffective due to the bulkiness of this cation.
To prove this surmise, try an electrolyte salt with a smaller cation - tetramethylammonium or even better a Lithium one and see whether You manage to measure a lower conductivity for the "dedoped" PEDOT-PSS. I don't know, however, which stable anion (PF6-, BF4-, ClO4-, CF3SO3-) lithium salt is soluble in acetonitrile. Can You switch to water based electrolyte solution instead?
The other option You may try is to hold PEDOT-PSS at -0.8V for some time (say 10, 20 or 30 minutes) and see if its conductivity decreases. The longer You apply the -0.8V potential to Your film, the more time the electrolyte cations will have to enter and penetrate the film.
Good luck,
Thanks a lot for your input Mr. Wojciech Domagala. I think this is worth trying.
However, In general we do spectroelectrochemistry of PEDOT-PSS under same conditions and able to dedope the films completely (confirmed by UV-vis spectra at each potential).
I am much more worried about the conductance in doped state (0.2 S) which will give conductivity of 20,000 S/cm if we divide it by 100 nm (thickness of the film). Generally reported in-situ conductivity for electropolymerized PEDOT is in range of 400 S/cm. Though PEDOT-PSS have conductivity of 1 S/cm (by four point probe measurements) and after PSS removal it becomes ~3000 S/cm, conductivity measured by electrochemical means can not give such a high value.
regards,
Rekha
Dear Rekha,
If You observe that You can dedope Your PEDOT-PSS films, then my whole previous elaboration simply looses ground...
I am actually not very well into the interdigitated electrode conductivity measurements, as I have embarked upon them only very recently.
One point of Your experimental protocol has raised my curiosity, however. You say You use 20mV potential offset between one interdigitated electrode's brush (working electrode 1) and the second brush (working electrode 2). Please note that in the case of easily dopable polymer like PEDOT-PSS, by setting the two electrodes 20mV apart, You actually create a doping level gradient between the two electrodes. That gradient will inherently induce an electron flow from the less doped part of the polymer to the more doped one. This current may top up the doped polymer capacitance current You measure and use to determine the conductivity of the PEDOT-PSS film, constituting a sheer bias. Please try using a lower potential offset between the two working electrodes (say: 1mV, 2mV or 5mV) and see what happens. The differences in working electrode 1 and working electrode 2 currents will, of course, decrease, but at such experimental regime, the doping level difference between the two electrodes will be minimised, and the parasite current supressed. I am curious myself, if this solution will help...
Good luck,
Kind regards,
Wojciech
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