Macroscopic Interfacial Property as a Determining Parameter for Reliable Prediction of Charge Mobility in Organic Transistors

Physical or chemical properties characterizing a surface of gate dielectric have a huge impact on the electrical properties of organic field-effect transistors. Here, we applied various organic interlayers between an organic semiconductor and a gate dielectric to describe field-effect mobilities being a function of a certain macroscopic parameter associated with the surface energy of gate dielectric. The organic interlayers with various chemical moieties, that is, hydroxyl, methyl, octadecyl, polystyrene, and polymethylmetacrylate, are obtained using diverse organosilane compounds and hydroxyl-end-terminated polymer brushes. Two prototypical vapor-deposited p-type organic small molecules, dinaphtho­[2,3-b:2′,3′-f]­thieno­[3,2-b]­thiophene and pentacene, are used as semiconducting layers. We separate the surface energy of the organic interlayers into two terms, that is polar and dispersive terms, and define three parameters consisting of these two terms, so-called surface energy ratio, polar ratio, and polarity. The three parameters are plotted with the field-effect mobilities and it becomes apparent that the field-effect mobility is a function of polar ratio and polarity regardless of the semiconducting material as well as its morphology and crystallinity. In particular, the polarity that is the polar energy term divided by the total surface energy showed a clear exponential relationship, allowing a reliable prediction of field-effect mobilities.