First-principles investigation of anisotropic electron and hole mobility in heterocyclic oligomer crystals.

Based on quantum chemistry calculations combined with the Marcus-Hush electron transfer theory, we investigated the charge-transport properties of oligothiophenes (nTs) and oligopyrroles (nPs) (n=6, 7, 8) as potential p- or n-type organic semiconductor materials. The results of our calculations indicate that 1) the nPs show intrinsic hole mobilities as high as or even higher than those of nTs, and 2) the vertical ionization potentials (VIPs) of the nPs are about 0.6-0.7 eV smaller than the corresponding VIPs of the nTs. Based on their charge-transport ability and hole-injection efficiency, the nPs have potential as p-type organic semiconducting materials. Furthermore, it was also found that the maximum values of the electron-transfer mobility for the nTs are larger by one-to-two orders of magnitude than the corresponding maximum values of hole-transfer mobility, which suggests that the nTs have the potential to be developed as promising n-type organic semiconducting materials owing to their electron mobility.