Overlapping, dangling sp3-hybridized orbitals are typical for
hydrocarbons exhibiting an alternating bonding structure.
These orbitals might either interfere constructively with p-conductive
bonding or destructively with n-conductive antibonding bands. In each
case the resulting conduction band can be imagined as a branched wave
function spreading across the sigma-bound molecular skeleton. Charges are
transported along these bands by thermally activated, incoherent
tunneling events. The technological relevance of pi-conjugated plastics
arises from their simple and cheap processability as compared to
silicon. Moreover, the fabrication of optoelectronic devices made of
plastics is more ecological. Organic thin-film transistors, light-emitting
diodes, lasers, and photovoltaic applications have already been
fabricated so far. However, many of these novel device architectures
suffer from severe technical problems, like that of low carrier mobility
and/or effects due to elusive device physics at bulk heterojunctions or
metal interfaces. Consequently the development of an efficient,
generally applicable and precise software to predict promising materials
and assemblies is indispensable. The insights gained by computer
experiments govern the fabrication of prototypes, in this way shortening
the developmental period remarkably. A three-dimensional kinetic Monte
Carlo simulator covering heterojunctions, molecular doping, metal
interfaces, image charge effects, interband transitions and arbitrary
space charge accumulations has been developed, tested, and optimized.
Baessler's Gaussian disorder model forms the computer program's
conceptual and theoretical basis. For calibration, the dark current
characteristics of zinc phthalocyanine have been used. The electrostatic
potentials are updated after each charge transfer. Organic
optoelectronic devices are usually contact-dominated. Thus the
development focused on the unified description of hopping injection,
conduction, and recombination and extraction of carriers.
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