15,553 research outputs found
Energetic disorder at the metal/organic semiconductor interface
The physics of organic semiconductors is dominated by the effects of
energetic disorder. We show that image forces reduce the electrostatic
component of the total energetic disorder near an interface with a metal
electrode. Typically, the variance of energetic disorder is dramatically
reduced at the first few layers of organic semiconductor molecules adjacent to
the metal electrode. Implications for charge injection into organic
semiconductors are discussed.Comment: 9 pages, 2 figure
Transient localization in crystalline organic semiconductors
A relation derived from the Kubo formula shows that optical conductivity
measurements below the gap frequency in doped semiconductors can be used to
probe directly the time-dependent quantum dynamics of charge carriers. This
allows to extract fundamental quantities such as the elastic and inelastic
scattering rates, as well as the localization length in disordered systems.
When applied to crystalline organic semiconductors, an incipient electron
localization caused by large dynamical lattice disorder is unveiled, implying a
breakdown of semiclassical transport.Comment: Revised version, to appear in Phys. Rev. B Rapid Communication
Hyperfine interaction and magnetoresistance in organic semiconductors
We explore the possibility that hyperfine interaction causes the recently
discovered organic magnetoresistance (OMAR) effect. Our study employs both
experiment and theoretical modelling. An excitonic pair mechanism model based
on hyperfine interaction, previously suggested by others to explain magnetic
field effects in organics, is examined. Whereas this model can explain a few
key aspects of the experimental data, we, however, uncover several fundamental
contradictions as well. By varying the injection efficiency for minority
carriers in the devices, we show experimentally that OMAR is only weakly
dependent on the ratio between excitons formed and carriers injected, likely
excluding any excitonic effect as the origin of OMAR.Comment: 10 pages, 7 figures, 1 tabl
Quantum coherence and carriers mobility in organic semiconductors
We present a model of charge transport in organic molecular semiconductors
based on the effects of lattice fluctuations on the quantum coherence of the
electronic state of the charge carrier. Thermal intermolecular phonons and
librations tend to localize pure coherent states and to assist the motion of
less coherent ones. Decoherence is thus the primary mechanism by which
conduction occurs. It is driven by the coupling of the carrier to the molecular
lattice through polarization and transfer integral fluctuations as described by
the hamiltonian of Gosar and Choi. Localization effects in the quantum coherent
regime are modeled via the Anderson hamiltonian with correlated diagonal and
non-diagonal disorder leading to the determination of the carrier localization
length. This length defines the coherent extension of the ground state and
determines, in turn, the diffusion range in the incoherent regime and thus the
mobility. The transfer integral disorder of Troisi and Orlandi can also be
incorporated. This model, based on the idea of decoherence, allowed us to
predict the value and temperature dependence of the carrier mobility in
prototypical organic semiconductors that are in qualitative accord with
experiments
Measuring Energetic Disorder in Organic Semiconductors Using the Photogenerated Charge-Separation Efficiency
Understanding and quantifying energetic disorder in organic semiconductors continues to attract attention because of its significant impact on the transport physics of these technologically important materials. Here, we show that the energetic disorder of organic semiconductors can be determined from the relationship between the internal quantum efficiency of charge generation and the frequency of the incident light. Our results for a number of materials suggest that energetic disorder in organic semiconductors could be larger than previously reported, and we advance ideas as to why this may be the case
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