Effects of gate dielectrics and their solvents on characteristics of solution-processed N-channel polymer field-effect transistors

In this study, we investigated the effects of polymer gate dielectrics and their solvents on the characteristics of n-channel top-gate-structured organic field-effect transistors (OFETs) that used poly{[N,N-9-bis(2-octyldodecyl)- naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)} (P(NDI2OD-T2)) (ActivInk™ N2200). The characteristics of P(NDI2OD-T2)-based OFETs are strongly dependent on the chemical properties of the polymer gate dielectrics used and the morphology of the semiconductor- dielectric interface, which is dependent of the dielectric solvent used for dielectric-layer deposition. Both spin-coated and inkjet-printed P(NDI2OD-T2)-based FETs exhibited reasonably high values of field-effect mobility (μ_FET) at 0.1-0.3 cm² V^-1 s ^-1 with poly(methyl methacrylate) as the gate dielectric and a number of carefully selected orthogonal solvents. The value of μ_FET decreased to 0.03 cm² V^-1 s^-1 for a solvent with poor orthogonality (1,2-dichloroethane). This was due to the semiconductor-dielectric interface being rough owing to the dissolution and/or swelling of the underlying P(NDI2OD-T2) layer. In addition, the value of μ_FET decreased dramatically, to 0.005 cm² V ^-1 s^-1, with poly(4-vinyl phenol) (PVP) as the dielectric material, dissolved in a perfectly orthogonal solvent (1-butanol). This was due to electron trapping by the hydroxyl groups in PVP.