tesi R. Miscioscia.pdf - EleA@UniSA

44 State of the Art
and other techniques which are inherently expensive, difficult to
maintain and scale-up and down. For this reason, as an instance,
starting from promising molecule pentacene (or other acene) through a
process of molecular functionalization, Anthony and others [16],
obtained high hole mobilities in field effect transistors thanks to the
high molecular order which the interaction of the functional groups
added to pentacene imposed to the molecules of the material deposited
(see figure 13).
figure 13: comparison between OFET devices performances obtained in functionalized pentacene
in relationship to ordering characteristics of modified molecules deposited films [16].
This depends on the degree of packing and order of the
molecules and, therefore, on how the π orbitals overlap along the
channel direction.
The goal of processes of functionalization of small molecules
for organic semiconductors is to insert functional groups and to use
solution processing allowing crystalline structures to self-assemble
into lattices increasingly extended thus improving the order and the
mobility and reducing the amount of defects.
An example of this is given by the study of Garnier on a still
widely used class of oligomers (thiophenes)[17]. Authors attempted
the formation of films with high mobility and, therefore, higher order