After having deposited all of the thin-films of photoactive materials on ITO/PET substrate to build a bulk-heterojunction solar cell (ITO/PEDOT/P3HT:PCBM/Al), I need to contact electrodes to make electrical carachterisation. It is easy to contact the outmost Al but: how can I contact the buried underlying ITO to make an effective electrical connection?
Adding on to what is already stated above, here are few tips I have found useful when I made the devices……..
You can either buy patterned ITO substrates or can etch the plain ITO substrates such that when you are making contacts for measurements you always contact either ITO on glass or Al (only Al) on glass. This can be done by etching away the ITO on one edge of your substrate where you plan to contact the Al electrode, and after spin coating the active layer wiping this contacting area with a cotton bud wetted with solvent.
The advantages of doing so are,
• When you try to contact Al on ITO there is a possibility of short circuiting your device, as the films are very thin and easily scratched off.
• Al on bare glass does not scratch off as easily as when it is on the polymer.
• When active layer is wiped off and Al is on bare glass, you can optionally add a dot of silver paint on Al without running into contamination problem for better contact. The need for this depends on the type of clips/contacts you are using.
• It is also possible to etch your substrate such that both your contacts are in ITO. Then you don’t need silver paint, and scratching off problems are not there. But on the down side you need a bit more complicated etching pattern, and sometimes the contact resistance can be a little higher due to long paths of ITO.
I would suggest electroplating gold. It is soft enough to not cause high film stress from CTE and makes reliable bond pads for multiple connection techniques.
You have few options:
1. If you you have minature probe heads, punch through or scratch the active layer with a sharp tungsten needle.
2. Remove a bit of material in the corner of your ITO/PET (e.g. with small cotton bud) and make contact with a tiny Au clamp/clip (you can buy them commercially).
3. Pattern your photoactive materials (e.g. use your Al contact as etching mask in oxygen plasma machine).
I would not use silver paints or conductive epoxy glues to attach wires because you would contaminate your photoactive materials.
Thank you Prof. Majewski.
I agree that one should avoid using silver paints and conductive epoxy glues in order to achieve an effective electrical connection.
Using a little bit of the solvent of your active layer remove small part of the thin film. Do it very carefully. One probe on Al and the another one on the ITO. If you have different Al lines on the same substrate it means you have different cells there, so check each one of them.
If you carefully design the ITO pattern and make Al contact onto the other side of ITO, then you would just need to probe at the ITO. Because sometimes Al is easy to be scratched.
you must read the document "The Fabrication and Characterization of
Organic Solar Cells of Scott Berkley, May 6, 2009 ".I will send it.
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