4 research outputs found
Identification of Ultrafast Relaxation Processes As a Major Reason for Inefficient Exciton Diffusion in Perylene-Based Organic Semiconductors
The
exciton diffusion length (<i>L</i><sub>D</sub>) is
a key parameter for the efficiency of organic optoelectronic devices.
Its limitation to the nm length scale causes the need of complex bulk-heterojunction
solar cells incorporating difficulties in long-term stability and
reproducibility. A comprehensive model providing an atomistic understanding
of processes that limit exciton trasport is therefore highly desirable
and will be proposed here for perylene-based materials. Our model
is based on simulations with a hybrid approach which combines high-level
ab initio computations for the part of the system directly involved
in the described processes with a force field to include environmental
effects. The adequacy of the model is shown by detailed comparison
with available experimental results. The model indicates that the
short exciton diffusion lengths of α-perylene tetracarboxylicdianhydride
(PTCDA) are due to ultrafast relaxation processes of the optical excitation
via intermolecular motions leading to a state from which further exciton
diffusion is hampered. As the efficiency of this mechanism depends
strongly on molecular arrangement and environment, the model explains
the strong dependence of <i>L</i><sub>D</sub> on the morphology
of the materials, for example, the differences between α-PTCDA
and diindenoperylene. Our findings indicate how relaxation processes
can be diminished in perylene-based materials. This model can be generalized
to other organic compounds