Controlling thickness depends on a lot of parameters. There are a lot of excellent papers that you can find for spin coating P3HT:PCBM to get started. To measure thickness you should use ellipsometry for non-destructive determination of thickness. You can use AFM for destructive determination of thickness.

THANKS, Dr.Sebastian Requena  for your answer

You can measure the resistivity of your material.

 thanks, Dr. Murat for your answer

Ellipsometer, profilometer or even an AFM (etch away a part of your film and take the step measurement) can be used to measure the thickness thin films.

thanks, Chumki for your answer

Dear colleague Dr. Amr,

Peace be up on you, your question's readers and all RG members

There three methods to check and measure film thickness; you can use one of the following according to condition of the film.

Film thickness can be checked by

1- An interferometric method, more details is available at: TOLANSKY S. Multiple beam interferometry of surfaces and films. London: Oxford University Press, 1988: 147.

2- Using mass of the film, m according to the next details::

W1 is the weight of cleaned substrate

W2 is the weight of cleaned substrate plus film

W2-W1= the weight of the film

ΔW=mg

m = ΔW/g

m=ρXV ; ρ, is the density of film material and V is the volume of the film

the Volume = (Width X Length X Thickness) of the film

3- SEM or AFM (film-substrate ) cross section

I wish this is useful and help you.

A. El-Denglawey

Thanks ,Prof Dr.Adel Eldenglawey for your answer