Control of charge transport in a semiconducting copolymer by solvent-induced long-range order

Recent reports on high-mobility organic field-effect transistors (FETs) based on donor-acceptor semiconducting co-polymers have indicated an apparently strong deviation from the paradigm, valid for a series of semi-crystalline polymers, which has been strictly correlating charges mobility to crystalline order. This poses a severe limit on the control of mobility and a fundamental question on the critical length scale which is dominating charge transport. Here we focus on a well-known model material for electron transport, a naphthalene-diimide based copolymer, and we demonstrate that mobility can be controlled over two orders of magnitude, with maximum saturation mobility exceeding 1 cm(2)/Vs at high gate voltages, by controlling the extent of orientational domains through a deposition process as simple as spin-coating. High mobility values can be achieved by adopting solvents inducing a higher amount of pre-aggregates in the solution, which through the interaction with the substrate, provide the polymer with liquid-crystalline like ordering properties.