Role of the HOMO-1 Orbital on the p-Type Charge Transport of the Fused-Ring Thienoacene DBTDT

The reported anisotropy of charge transport for the fused ring thienoacene dibenzo-thieno-dithiophene (DBTDT) is explained in terms of the role of a second occupied molecular orbital lying very close to the HOMO orbital and displaying remarkable electronic couplings for charge transport along the c crystallographic axis. The origin of the HOMO/HOMO-1 proximity is rationalized by considering a series of dibenzo-thieno-N-thiophene homologues. Embedding effects are shown to decrease further the energy difference between the HOMO and HOMO-1, thereby enhancing the role of the latter as a possible source of competing charge carriers. Thermally induced disorder effects lead to minor fluctuations of the HOMO electronic couplings but activate crossed couplings between the HOMO and HOMO-1, thereby allowing the generation of both charge carriers during charge propagation.