Dear Abdolhossei,

Pentacene is an organic small molecule so it is deposited by thermally evaoprating the powder. If you want to thin film using spin coating then choose soluble molecule. The pentacene is not easily soluble to any solvent. So you will not excellent uniformity in the film.

thanks

Are you have any paper or idea for thermally evaoprating of this powder? 

Ideally you want to sublimate under vacuum, rather than simply evaporate. I don't have a paper to hand, but first find out if you have the equipment available. Typically something like this

http://www.london-nano.com/cleanroom-and-facilities/equipment/edwards-a306-belljar-evaporator