(394a) Sublimation Mechanism for Small Molecule Organic Semiconductors

Sublimation Mechanism
for Small Molecule Organic Semiconductors

Yi Zhang, Nathan T.
Morgan, Russell J. Holmes, and Edward L. Cussler

Department of
Chemical Engineering and Materials Science

University of
Minnesota, Minneapolis MN 55455

Organic semiconductors continue
to receive substantial application for next-generation display, photovoltaic
and solid-state lighting technologies. Processes capable of producing high
purity materials at large scales are desirable. Presently, the majority of these
materials are purified using thermal gradient sublimation.  We find that
the sublimation rate of the archetypical, small molecule hole transport
material N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (NPD), is
controlled by a combination of viscous flow and physical vapor
deposition.  Other steps like diffusion within the solid feed, reaction at
the feed particle surface, and mass transfer within the bed of feed particles
do not significantly affect the sublimation rate.  Such a mechanism is in
contrast with other commercially practiced sublimations.  The results
obtained here for NPD suggest guidelines for the large-scale purification of
active materials for organic electronic devices.