Transistor Characteristics of Charge-Transfer Complexes Observed across a Neutral-Ionic Transition.

For basic understanding of transistor properties of doped organic semiconductors, 3,3',5,5'-tetramethylbenzidine charge-transfer complexes are investigated, which change from neutral to ionic by varying the acceptors. When going into the ionic state, the bulk conduction increases more rapidly than the mobility, but sufficiently thin devices exhibit transistor properties. The resulting ambipolar characteristics are analyzed in the linear regions at small drain voltages in analogy with graphene transistors.

Carrier Charge Polarity in Mixed-Stack Charge-Transfer Crystals Containing Dithienobenzodithiophene.

Dithieno[2,3- d;2'3'- d']benzo[1,2- b;4,5- b']dithiophene forms mixed-stack charge-transfer complexes with fluorinated tetracyanoquinodimethanes (F TCNQs, n = 0, 2, and 4) and dimethyldicyanoquinonediimine (DMDCNQI). The single-crystal transistors of the F TCNQ complexes exhibit electron transport, whereas the DMDCNQI complex shows hole transport as well. The dominance of electron transport is explained by the superexchange mechanism, where transfers corresponding to the acceptor-to-acceptor hopping ( t) are more than 10 times larger than the donor-to-donor hopping ( t).