Nature And Extent Of Solution Aggregation Determines The Performance Of P(Ndi2od-T2) Thin-Film Transistors

Here the effect of solvent quality on the microstructure and organic field-effect transistor (OFET) performance of thin films of the high mobility naphthalene-diimide-thiophene-based n-type semiconducting copolymer P(NDI2OD-T2) is investigated. A strong correlation between OFET mobility and solvent quality is observed with average electron mobility increasing from 0.21 cm(2) V-1 s(-1) for samples prepared from tolerably good solvents to 0.56 cm(2) V-1 s(-1) for samples prepared from poor solvents, with a maximum electron mobility of 1.5 cm(2) V-1 s(-1) observed for transistors processed from toluene. The variation in transistor performance with solvent quality is linked to the nature and extent of the solution aggregation of P(NDI2OD-T2) chains. Small angle X-ray scattering measurements reveal elongated rod-like aggregates up to 300 nm in length in solutions prepared using poor solvents, in contrast to more coil-like chains with radius of gyration of approximate to 10-15 nm for solutions based on good to tolerably poor solvents. Thin films produced from decreasing solvent quality show an increase in the extent of correlated ordering of backbones and the degree of edge-on orientation of polymer chains at the air/film interface. This work establishes the important link between solution-phase chain aggregation behavior, thin-film microstructure, and transistor performance in the P(DNI2OD-T2) system.