Some researchers said they stir for overnight, some said just for few hours. I think this stir is to ensure the p3ht:pcbm dissolve in a solvent. In addition, some researchers said that the p3ht: pcbm must be heat at 60 and some said no need heating avoiding anaerobic condition. Can I know what the effect of these two ( stirring time and heating) on p3ht: pcbm?
As you said long stirring and heating are used to dissolve the materials. Especially high molecular weight P3HT can take a long time to dissolve. As longer stirring is normally not harmful for the solution, people leave it stirring overnight to be sure everything is fully dissolved. Alternatively heating can be used.
I agree with Michiel, it depends on your molecular weight but overnight is better to make sure the polymer is fully dissolved. However, stirring at 60 C for a few hours should also work if you are short of time. It is better to protect your solution from the light in either case. Good luck!
I agree for both Michiel and Sarah.
Longer stirring help for dissolving while heating make it faster dissolve.
In case of solar cell, f you compare both short stirring with 60C and long stirring with 60C for your P3HT:PCBM solution, i believe they is no big different in your efficiency.
It also depends on the solvent you used. I stir them overnight for chlorobenzene, however it requires a shorter time for dichlorobenzene. PCBM has a higher solubility rate in dichlorobenzene than chlorobenzene.
Usually a couple of hours at 60 degrees are enough to dissolve both P3HT (even high Mw up to 200 000) and PCBM in either chlorobenzene or dichlorobenzene. An easy way to check if you have properly dissolved your materials (which is also good for device performances) is to filter with 200 nm porous membranes. If you need to push hard through the filter than your P3HT is not dissolved entirely.
Note that the above mentioned comments are for solutions up to 45 mg/ml (P3HT+PCBM).
If by any chance you use chloroform (not recommended at all), do not heat at 60 degrees as this will likely change your solution concentration (even if you ensure that everything is tightly capped).
Heating overnight ensures that complete dissolution is achieved but keep in mind that if you‘re not using a glovebox, it might also partially oxidize your materials.
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