High-mobility air-stable solution-shear-processed n-channel organic transistors based on core-chlorinated naphthalene diimides

Abstract

High charge carrier mobility solution-processed n-channel organic thin-film transistors (OTFTs) based on core-chlorinated naphthalene tetracarboxylic diimides (NDIs) with fluoroalkyl chains are demonstrated. These OTFTs were prepared through a solution shearing method. Core-chlorination of NDIs not only increases the electron mobilities of OTFTs, but also enhances their air stability, since the chlorination in the NDI core lowers the lowest unoccupied molecular orbital (LUMO) levels. The air-stability of dichlorinated NDI was better than that of the tetrachlorinated NDIs, presumably due to the fact that dichlorinated NDIs have a denser packing of the fluoroalkyl chains and less grain boundaries on the surface, reducing the invasion pathway of ambient oxygen and moisture. The devices of dichlorinated NDIs exhibit good OTFT performance, even after storage in air for one and a half months. Charge transport anisotropy is observed from the dichlorinated NDI. A dichlorinated NDI with -CH(2)C(3)F(7) side chains reveals high mobilities of up to 0.22 and 0.57 cm(2) V(-1) s(-1) in parallel and perpendicular direction, respectively, with regard to the shearing direction. This mobility anisotropy is related to the grain morphology. In addition, we find that the solution-shearing deposition affects the molecular orientation in the crystalline thin films and lowers the d(001)- spacing (the out-of-plane interlayer spacing), compared to the vapor-deposited thin films. Core-chlorinated NDI derivatives are found to be highly suitable for n-channel active materials in low-cost solution-processed organic electronics.