Theoretical modelling of carrier transports in molecular semiconductors: molecular design of triphenylamine dimer systems

Charge transport in molecular systems and biosystems can be different from that in inorganic, rigid semiconductors. The electron-nuclear motion couplings play an important role in the former case. We have developed a theoretical scheme to employ the Marcus electron transfer theory coupled with a direct diabatic dimer model and the Brownian diffusion assumption to predict the carrier mobility for molecular materials. For triphenylamine, a typical molecular transport material, the design strategies regarding the formation a cyclic or a linear dimer are evaluated from theoretical calculations for the carrier mobility. We made a comparison between the mobility and the electrical polarizability. It is found that in the case of triphenylamine dimer, these two quantities have different trends. The fact that the macrocycle possesses higher mobility but lower polarizability than the linear chain is due to the difference in the reorganization energy. The theoretical predicted temperature dependences are analysed within the hopping mechanism. The calculated room-temperature mobilities are in reasonable agreement with experimental values.