tesi R. Miscioscia.pdf - EleA@UniSA

Chapter 2 39
deposition process of the OSC. In fact, electrical and structural
properties of the semiconducting film can change if deposited on a
metal surface or not. As an instance, theoretical and experimental
studies [8][9] prove that a gold deposition on pentacene shows traces
of metal diffusion in the OSC film reducing the electrical potential
barrier at the contact-channel interface.
2.4 Organic conductors and channel
semiconductors
At a first glance, a material’s conductivity is proportional to
the product between the concentration of free charge carriers and their
mobility in the abovementioned material. The physical parameters that
drive such charge density are summarized as follows:
• The thermally-activated intrinsic mobile charge population
in the material (depending on the temperature T and the
bandgap energy Eg);
• The extrinsic carrier population due to a wanted/unwanted
doping of the material;
• The eventual presence of an optical excitation;
• The Field-Effect;
• The charge injection;
Nevertheless, it’s necessary to take into account the link
between the charge mobility and the following factors:
• Charge transport phenomenons;
• The presence of charge traps;
• The molecular order of channel semiconductor
Also for these reasons the Organic Electronics world is always
changing in the quest for the optimal combination among the virtually
unlimited mixes between organic conductors and their dopants which
as an instance can change a low-conductance polymer (in common