I have spin coated PEDOT-PSS films on ITO. When I do cyclic voltammetry of these films, they show a huge change in CV after every cycle especially change in the reduction peak current (decreases) and potential (towards more positive). Can anyone suggest the possible reason and solution of this problem? Is this normal behavior of such films since I couldn't find any such information in literature. It seems that films are becoming resistive after each cycle.
Your CV looks fine, but I don't think if you need to go down to -1.2V. At this potential you may reduce air instead of PEDOT.
If you want to know whether you are reducing PEDOT at that potential or not, easily you can watch the film color while you are running CV.
PEDOT is sky blue at its oxidized state. When its being reduced the color changes to dark blue. So, if the color transition (you can see that by your eye) occurs at around -1V , you are reducing PEDOT at this potential. If not (earlier) this peak is not for PEDOT reduction.
If you want to do more accurate measurement, do that in situ inside the UV-VIS.
Thanks Christian, I will definitely try this. I always do normal N2 purging (15-20 min.) before CV measurements. This material shows different absorption in oxidized and reduced state. It should come back to the same absorption value after each redox cycle but I see simultaneous decrease in absorption especially for the reduced state which indicates that after each cycle films is not getting reduced like the earlier one (absorbance is lesser). There is increase in film resistance after doing CV. Though, such decrease in reduction and oxidation peak current happen in PEDOT films but after many cycles. This materials is know for its high cyclic stability.
Your CV looks fine, but I don't think if you need to go down to -1.2V. At this potential you may reduce air instead of PEDOT.
If you want to know whether you are reducing PEDOT at that potential or not, easily you can watch the film color while you are running CV.
PEDOT is sky blue at its oxidized state. When its being reduced the color changes to dark blue. So, if the color transition (you can see that by your eye) occurs at around -1V , you are reducing PEDOT at this potential. If not (earlier) this peak is not for PEDOT reduction.
If you want to do more accurate measurement, do that in situ inside the UV-VIS.
Thanks a lot for your comments. I do in-situ UV-VIS also along with the electrochemical switching. I observe a fast decrease in the absorbance of reduced state after each CV cycle. These films are not stable on electrochemical cycling. I do same study for electropolymerized PEDOT too but they are much more stable (both CV and absorbance) compared to PEDOT-PSS. Electropolymerized PEDOT also shows decrease in reduction and oxidation peak current and corresponding decrease in absorbance of reduced state but slower compared to PEDOT-PSS films. I have no idea how much stable are these films (both PEDOT-PSS and electropolymerized PEDOT) in general. In few references especially for electropolymerized PEDOT, optical switching has been shown and it seems to be fairly stable. Is something wrong with the reference electrode or auxiliary or my electrochemical cell (contacts) ? I am not able to figure out.
I have attached Optical switching of PEDOT-PSS films.
Do you do the CV in aqueous or organic electrolyte? In aqueous you may wash away some of your PEDOT.
Have you done any solvent (ethylene glycol, DMF, etc) treatment on your PEDOT:PSS film. Simply wet the film with one of these solvent then dry thw film at 120-150oC for 0.5h. After this the conductivity and stability of the PEDOT:PSS increase significantly.
Also you can see: Advanced Functional Materials 21 (17), 3363-3370
Thanks!
I use acetinitrile with TBAP electrolyte. I will try the treatment of PEDOT-PSS films and let you know the results. My main concern is decreasing absorbance of reduced state of PEDOT-PSS during optical switching. I went for higher negative potential (up to -1.2 V because I saw increase in absorbance even beyond -1 V (vs Ag/Ag+). I will try to cycle the films in narrow potential range (-1V to 0.8 V) and see if CV is stable or not. Thanks for the reference. It is real informative.
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