Phase dependence of hole mobilities in dibenzo-tetrathiafulvalene crystal: A first-principles study

The organic semiconductor dibenzo-tetrathiafulvalene (DBTTF) has presented different polymorphs in solid packing, but the structure-property relationship is little clarified in the literature which is important for the design of high-performance organic semiconductors. In this study, the charge transport in DBTTF crystals for the α phase and β phase is investigated from the first-principles calculations and the Marcus charge transfer theory. The one-, two- and three-dimensional mobilities are obtained simultaneously from a set of identical trajectories with an improved random walk technique. It is found that the α-phase crystal presents a smaller three-dimensional mobility than that in the β-phase crystal although the mobility is much large along the c axis in the α-phase crystal. This is attributed to that the electronic couplings are mainly confined within the c axis for the α-DBTTF while the electronic couplings are more uniform in the three-dimensional space for the β-DBTTF which thus provides more transport pathways for the charge transport. As a result, the β-DBTTF may have a larger potential for practical applications in organic electronics.