Hopping Mechanism

Abstract

In the limit of strong electron-phonon coupling and weak intermolecular electronic coupling, a charged molecule undergoes a large geometry relaxation, which eventually traps the charge. In this case, the charge transport can be viewed as an intermolecular hopping process. With the known electron transfer rates between neighboring molecules, the charge carrier mobility can be evaluated through the Einstein relation from random walk simulations. In general, the classical Marcus electron transfer theory, which works well in the high-temperature limit. For a better understanding, we incorporate the nuclear tunneling effect arising from the intramolecular high-frequency vibrations to characterize the transport behavior at room temperature. Dynamic disorder effect arising from the intermolecular low-frequency vibrations is found to be very much materials structure or space-dimension dependent, which may give rise to the phononassisted current.Keywords Hopping mechanism Á Marcus electron transfer rate Á Random walk simulation Á Temperature dependence of mobility Á Nuclear tunneling Á Dynamic disorder In Sect. 2.1, we describe the general methodology to simulate the hopping mobility using the electron transfer rate formalism. This approach is applied to different organic materials and discussed in Sects. 2.2, 2.3, 2.4. Section 2.5 investigates the nuclear tunneling effect of the intramolecular vibrations, and finally Sect. 2.7 is about the dynamic disorder effect of the intermolecular modes. For each of these improvements, application examples are presented in Sects. 2.6 and 2.8, respectively.Z. Shuai et al.,

Remarkable charge-transfer mobility from [6] to [10]phenacene as a high performance p-type organic semiconductor

“…It is suggested that in an extreme case, when the fluctuation in the transfer integral is larger than its average, the dynamic disorder can even increase the hole mobility for 2D materials within the ab-plane. 59 Nevertheless, despite of its limitation, Marcus theory has been widely used to describe the charge transfer mechanism in various organic materials at room temperature and shows good agreement with the experiments. 36,38,60 The inclusion of dynamic disorder will be considered in our future work for further improvement of the calculated mobility in organic semiconductors.…”

“…A phonon-assisted term needs to be added to the temperature dependence of mobility. 59 However, such type of calculation is computationally expensive in the study of 3P-10P or even larger phenacene structures. It is suggested that in an extreme case, when the fluctuation in the transfer integral is larger than its average, the dynamic disorder can even increase the hole mobility for 2D materials within the ab-plane.…”