The transport of charge carriers through organic semiconductors (OS) is at the heart of many exciting technologies suchas organic electronics, organic light-emitting diodes and photovoltaics, and nanobioelectronics. Over the past 10 years importantprogress has been made by several research groups towards theory andcomputational modeling of charge transport (CT) in OS[1–7]. However, the nature of excess electrons and electron holes in these materials, as well as their transport mechanism, are still not very well understood. This is because CT in OS is often in a difficult regime where standard theories such as band theory and small polaron hopping models are inapplicable. To address this problem, we have recently developed a computationally efficient non-adiabatic molecular dynamics method for the simulation of charge carrier transport in OS, termed fragment orbital-based fewest switches surface hopping (FOB-SH)[8]. This methodology makes no assumptions regarding the CT mechanismand can describe a broad spectrum of possible transport regimes.

In our contribution we briefly describe the FOB-SH methodology and present first applications to CT in 1D chains of organic molecules. In particular we discuss the behavior ofcharge mobility versus temperature (T) for different regimes of the intermolecular electronic coupling. For small couplings FOB-SH predicts a crossover from a thermally activated regime at low temperaturesto a band-like transport regime at higher temperatures. For higher electronic couplings the thermally activated regime disappears and themobility decreases according to a power law as T ^-n, where n is about 2, as often observed experimentally in ultrapure organic crystals. This is interpreted by a gradual loss in probability for resonance between the sites as the temperature increases. The popular polaron hopping model commonly used in the literature gives a qualitatively different result and strongly underestimates the mobility decay at higher temperatures. These first results are very promising for future applications of FOB-SH to CT in organic crystals, thin films and donor-acceptor layers of real devices.

References:

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[3] A. Troisi, A. Cheung, D. L. Andrienko, D. Phys. Rev. Lett. (2009)

[4] A. Troisi, Chem. Soc. Rev. (2011).

[5] L. Wang and D. Beljonne, J. Phys. Chem. Lett. (2013).

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[8] J. Spencer, F. Gajdos, J. Blumberger, submitted (2016).