Efficient High Area OFETs by Solution Based Processing of a π-Electron Rich Donor

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 cm 2 /V s for a channel length L = 100 μm and about 0.01 cm 2 /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 cm 2 /V s with an on/off ratio of the order of 10 4 .