Theoretical Studies of Bipolar Transport in CnBTBT-FmTCNQ Donor-Acceptor Cocrystals.

The development of crystals with bipolar transport characteristics is essential for high-performance organic field effect transistor (OFET) devices. In this work, we theoretically investigated the bipolar transport behaviors in CnBTBT-FmTCNQ cocrystals. It is found that bipolar transport can be realized in C8BTBT-TCNQ and C12BTBT-TCNQ cocrystals with room-temperature electron/hole mobility up to 1.8/0.75 and 2.5/1.8 cm2 V-1 s-1, respectively. The comparable electron- and hole-transfer integrals between the nearest-neighbor molecule pairs as well as the small hole reorganization energy of the TCNQ molecule are responsible for the balanced electron and hole mobilities. Moreover, because of the π-π stacking between neighboring molecules, all cocrystals show strong anisotropic transport characteristic for both electron and hole transport with the mobility along the π-π stacking direction much larger than those along the other two directions. This work provides the possibility of high-performance OFET engineering and also enriches the OFET families with bipolar transport characteristics.