Crystal Chemistry at the Molecule-Substrate and Molecule-Molecule Interface in Organic Electronic Systems

The exploration and understanding of the crystallization, growth and the orientation
of organic molecules on substrates is a very important feature in fundamental as well
as applied research in the various fields of organic electronic device research. It is
well known that the ordering and orientation of organic molecules significantly affects
the electronic structure and transport properties, and the anisotropy of the transport
properties in organic semiconductor thin films in particular has to be taken into account.
It is, however, not only the orientation of the film as a whole that is important, but the
molecular orientation in the few layers near an interface to other device layers that may
affect the electronic properties, such as the electronic trap states, contact resistances or interface dipoles.
In this lecture, I will discuss our efforts in investigating charge and photogenerated
transport at organic nanocrystalline interfaces. For example, we have synthesized single-crystalline donor-acceptor nanowire devices (i.e. transistors, solar-cells) that have enabled us to demonstrate excitonic charge splitting and ambipolar charge transport at p-n nanointerfaces. The use of organic single-crystalline devices will have a major impact in accelerating the emerging area of organic electronics, as these highly ordered systems will enable one to extract intrinsic charge carrier transport phenomena that cannot be accurately determined from disordered systems common to amorphous and/or polycrystalline films used in mainstream devices.