Dear colleague,
I try to make opv device using PTB7:PC70BM active layer. The solvent/additive of this active solution are Chlorobenzene and DIO. When I try to spin-coat a phosphomolybdic acid (PMA) solution on active layer film, sometime the white circle flake appears and sometime not.
Note : I have try various concentrations from low to high concentration, but sometime the problem is still occured.
What is the reason behind this phenomenon and how to solve this problem? Here I also attached the picture of my experiment condition
thank you
Dear Adi,
welcome!
Most probable that the PMA solution redissolves the active layer. For that , you have to investigate the reaction of the active layer with PMA. It is well known procedure to use process compatible materials.
Best wishes
Hi,
As Prof. Zekry concluded, the active layer might be soluble in PMA, so his suggestion to just go for a quick test to see the effect of PMA on the active layer is very helpful.
If you really wanna use the PMA on top of the active layer you can dilute it in alcohol (Methanol or IPA, or other kind) and try to spin it at high speed. You can also anneal you active layer for 10 min ( I do not know what is the effect of annealing on your device performance) and spin coat your diluted PMA. You can also use cross-linking agent to prevent your active from dissolving in PMA (this is the last option to try).
If you are using PMA as buffer layer, you can invert your device structure.
Good luck,
Farahat
Hi Adi,
The others have already given you adequate answers. You need to check the orthogonality of your solvent/additive and the PMA solution. If they are not, it simply means that the PTB7:[70]PCBM is somewhat soluble in PMA too. Thus, PMA redisolves your active layer. Check the paper with link below for better understanding of the topic and concept:
Article Identifying orthogonal solvents for solution processed organ...
Best,
Dear Adi,
Have you tried to spin-coat the pure solvent in which PMA is dissoved?
Alexander Pud yes sir, there is no problem when I spin-coat IPA on active layer
It means that PMA interacts with PTB7. In particular PMA can oxidize this donor polymer.
Sometimes, high molecular weight of PTB7 create a problem for solubility.
I think annealing will degrade the performance (@Farhat) and will not work out. I think IPA will be the best option for this.
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