Prediction of remarkable ambipolar charge-transport characteristics in organic mixed-stack charge-transfer crystals

Figure Persented: We have used density functional theory calculations and mixed quantum/classical dynamics simulations to study the electronic structure and charge-transport properties of three representative mixed-stack charge-transfer crystals, DBTTF-TCNQ, DMQtT-F ₄TCNQ, and STB-F ₄TCNQ. The compounds are characterized by very small effective masses and modest electron-phonon couplings for both holes and electrons. The hole and electron transport characteristics are found to be very similar along the stacking directions; for example, in the DMQtT-F ₄TCNQ crystal, the hole and electron effective masses are as small as 0.20 and 0.26 m ₀, respectively. This similarity arises from the fact that the electronic couplings of both hole and electron are controlled by the same superexchange mechanism. Remarkable ambipolar charge-transport properties are predicted for all three crystals. Our calculations thus provide strong indications that mixed-stack donor-acceptor materials represent a class of systems with high potential in organic electronics.