Theoretical study on the charge transport and metallic conducting properties in organic complexes

Abstract

The charge transfer process between substrate molecular and dopant always appears in doped organic semiconductors, so that molecular doping is a common method to improve the electrical properties by combining appropriate complexes of electron acceptor and donor molecules. At the interface of the doped complexes, the amount of charge-transfer based on the charge analysis method could be affected by various factors, including the stacking structure, the HOMO_D–LUMO_A gaps, the offset defined by the donor ionization potential and the acceptor electron affinity IP_D–|EA_A|, and the strength of the intermolecular orbital interaction. To better understand the charge transport properties in complex crystals, reasonable mobility values were calculated by combining semi-classical Marcus–Hush theory with molecular dynamics simulation, in which the mobility values were on the same order of magnitude as experimental values. The largest and average room-temperature mobility were 4.59 and 0.21 cm² V⁻¹ s⁻¹ for TTF–TCNQ based on the anisotropic transport properties and random-walk schemes of the charge diffusion coefficient. The interface of the TTF–TCNQ crystal possesses metallic conducting properties with a predicted resistance of 4.43 kΩ. Charge-transfer complexes exhibit larger mobility and higher conductivity compared to the constituent donor and acceptor molecules.