We report on the preparation of high performance field-effect transistors (FETs) based on large areas of aligned films of a TTF derivative, namely, tetrakis-(octadecylthio)-tetrathiafulvalene (TTF-4SC18). TTF-4SC18 assembles into one-dimensional stacks in which the long alkyl chains promote intermolecular π−π overlapping due to their extremely closely packed nature. The films were prepared from solution by zone-casting, a simple technique that does not require the use of preoriented substrates. The films were characterized by AFM and X-ray, indicating an extremely high crystalline quality. The TTF molecules are tilted with respect to the substrate surface and are well-aligned in the casting direction. More than 40 FETs were measured, showing a remarkable reproducibility of their performance. The average charge carrier mobility value measured along the casting direction was about 0.006 cm2/V s for a channel length L = 100 μm and about 0.01 cm2/V s for L = 80 μm and L = 50 μm. The FET mobilities determined in the direction perpendicular to the orientation were ca. 1 order of magnitude lower. We found that all the devices after annealing exhibited an enhanced performance with FETs mobilities about 1 order of magnitude higher. The best devices revealed a charge carrier mobility close to 0.1 cm2/V s with an on/off ratio of the order of 104.

In this paper we present that the surface energy of silicon dioxide employed as the dielectric in bottom gate organic field effect transistors has large impact on the device performance. By the use of the zone-casting simple solution processing technique, we ensured reproducibility of active layer preparation confirmed by the atomic force microscopy and x-ray diffraction that showed high crystalline quality. Electrical measurements revealed that charge carrier mobility based on highly ordered zone-cast tetrakis-(octadecylthio)-tetrathiafulvalene layer was increased 30 times to 0.2 cm2/V s, when dielectric surface energy decreased from 51.8 to 40.1 mN/m.

In organic electronics solution‐processable n‐channel field‐effect transistors (FETs) matching the parameters of the best p‐channel FETs are needed. Progress toward the fabrication of such devices is strongly impeded by a limited number of suitable organic semiconductors as well as by the lack of processing techniques that enable strict control of the supramolecular organization in the deposited layer. Here, the use of N,N′‐bis(4‐n‐butylphenyl)‐1,4,5,8‐naphthalenetetracarboxylic‐1,4:5,8‐bisimide (NBI‐4‐n‐BuPh) for fabrication of n‐channel FETs is described. The unidirectionally oriented crystalline layers of NBI‐4‐n‐BuPh are obtained by the zone‐casting method under ambient conditions. Due to the bottom‐contact, top‐gate configuration used, the gate dielectric, Parylene C, also acts as a protective layer. This, together with a sufficiently low LUMO level of NBI‐4‐n‐BuPh allows the fabrication and operation of these novel n‐channel transistors under ambient conditions. The high order of the NBI‐4‐n‐BuPh molecules in the zone‐cast layer and high purity of the gate dielectric yield good performance of the transistors.