Theoretical investigations of electronic structure and charge transport properties in polythiophene-based organic field-effect transistors

Regioregular poly(3-hexylthiophene) (P3HT) is a hole transport polymer material used in organic field-effect transistors (OFETs) and can reach mobilities as high as 0.1 cm(2) V-1 s(-1). Factors that affect the charge mobility and the transport mechanisms of P3HT-based OFET systems are therefore of great importance. We use quantum mechanical methods to interpret the charge mobility and the transport properties of self-assembled P3HT molecules along the intra-chain and inter-chain directions. Our approach is illustrated by a hopping transport model, in which we examine the variation of charge mobility with torsional angle and the intermolecular distance between two adjacent thiophene segments. We also simulate packed P3HT structures via molecular dynamics (MID) simulations. The MD results indicate that the resultant mobility along the pi - pi inter-chain direction is significantly less than that along the intra-chain direction. Accordingly, the main charge-transfer route within the P3HT ordered domains is an intra-chain rather than an inter-chain one. The calculation result for the inter-chain hole mobility is around 10(-2) cm(2) V-1 s(-1), which is consistent with experimental data from P3HT single fibril. (C) 2009 Society of Chemical Industry