we deposit Aluminum on conjugated polymer surfaces to develop the cathode on the solar cell.
the structure of a typical device is: Glass/ITO/PEDOT:PSS/(P3HT:PCBM blend)/LiF/Al
LiF is not present all the cases but mostly. the evaporation is done thermally using tungsten filaments, the vac. level is ~5e-7mbar. all this happens in a glove box (N2 atmosphere)
questions:
1- what are the conditions (parameters) that would result in a uniform dense coating
2-does the Al vapors damage the polymer (conjugation etc)
3-how can we minimize damage to the polymer/Al interface (if any) due to the hot Al flux or extra heat produced by the filaments
suggestions are highly appreciated. thanks in advance

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1a. Uniformity - depends on the area. The vapor source is essentially from a point source and the thickness will depend on the angle between a point on the substrate and the source. If it is a large area you may have to move the substrate in a pattern over the source.

1b. Density - Greatest density will be when you have the deposition flux normal to the surface.

2. Don't know - see 3

3. Depends on how sensitive the polymer is. There will be the condensation energy and the radiant energy from the source. Use a shutter to minimize the radiant heating.

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Thank you for the reply.
answer 1b: does that depend on the distance between the source and the substrate too? my source and substrates surfaces are normal!

On a different note:
I want to deposit LiF (lithium floride) on a substrate and calculate the tooling factor for my set up. I can not get a qood film. very poor coverage. looks like some islands/particles and not connected film. I am using Si substrate. can you pls. suggest any modification to this process to get a nice coverage. thanks

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1b: if there is gas scattering there will be a less dense film.

LiF: Ref: Ionization-assisted deposition of LiF electron-injection layer for organic light-emitting diodes, Kuniaki Tanaka, Miyuki Amou, and Hiroaki Usui, J. Vac. Sci. Technol. B 22, L1 (2004). They found that LiF deposited as islands unless they used IAD. You might try exposing the Si to a plasma and see if that cleans the surface and perhaps generates some nucleation site from the UV in the plasma (assuming that you are using un-doped Si).

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