I need to fabricate organic solar cells. The organic materials I'm using are soluble in Chlorobenzene (PCBM, P3HT, PCDTBT, and etc.)
I'm doing some tests in order to obtain uniform layers on top of the PEDOT:PSS.
As a start I used a Chlorobenzene solution with 20mg/ml PCBM.
So far I could not get a uniform layer, sometimes the edges are not covered well (12*12mm square glass substrate), sometimes there are small spots, and sometimes it seems like there are some areas with different thicknesses. Some pictures are attached below.
Does someone have some experience on that matter that he can share?
The PEDOT:PSS was spin-coated after 0.45um filtration to get an approximately 30nm layer, and then heated to 105 degrees outside and inside the glove-box.
I used an anhydrous 99.8% Chlorobenzene and used 0.45um filter before spin-coating the PCBM layer.
I would propose that you deposit your active layer solution in chlorobenzine directly in a very clean glass surface. In this way you can verify the homogeneity of your active layer and the best mixing ratio as well as the required viscosity and spin speed.
May be the the inhomogeneous PEDOT:PSS underlying layer is the cause of the appearance of the inhomogeneous active layer.
What is the light brown colored area in your film. It has specific geometry. From where it comes???
For treating the glass before coating with PEDOT:PSS please follow the link: https://www.researchgate.net/post/Why_pedot_pss_do_not_adhere_on_ITO_substrate_while_spin_coating
Best wishes
I would propose that you deposit your active layer solution in chlorobenzine directly in a very clean glass surface. In this way you can verify the homogeneity of your active layer and the best mixing ratio as well as the required viscosity and spin speed.
May be the the inhomogeneous PEDOT:PSS underlying layer is the cause of the appearance of the inhomogeneous active layer.
What is the light brown colored area in your film. It has specific geometry. From where it comes???
For treating the glass before coating with PEDOT:PSS please follow the link: https://www.researchgate.net/post/Why_pedot_pss_do_not_adhere_on_ITO_substrate_while_spin_coating
Best wishes
Thank you, the substrate is a glass+ITO, this light brown area is the ITO. I didn't inspected the PEDOT:PSS with a microscope but the PP seems quite uniform.
Dear Dor,
I faced the same problem before. I think it because of the low adhesion of the PEDOT:PSS surface. Heat the substrate before the PCBM spin coating can be very useful. And, after you drop the PCBM solution on the substrate, you have to spin coating immediately and move ASAP.
@Leiping Duan, do you think I need to first start to spin and then drop the PCBM or first put the PCBM and then start spinning?
I read that heating is not recommended since the Chlorobenzene can evaporate more quickly but I'll give it a try, thanks for the suggestions
Heating is acceptable for CB, what I usually do in my lab to increase adhesion is that use hot glass substrates and even hot PCBM solution when spin coated.
In your case, you can try first start spin then drop. The condition in your picture is usually results from that the time between the drop of the PCBM and the spin is too long. If you first drop and then spin, you have to move fast and spin immediately!
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