Search

We present the first characterization of single-crystal devices of a new solution processable material that we have previously demonstrated achieves technologically relevant performance in the polycrystalline thin film state. Our studies include growth and investigation of structural, as well as electronic properties of single crystals of 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TESADT). Field-effect transistors fabricated on the surface of diF-TESADT single crystals exhibit excellent electronic properties: mobility as high as 6 cm 2/Vs, large current on/off ratios ( Ion/ Ioff= 1 × 10 8), small subthreshold slopes ( S= 1 V/dec), and extremely small hysteresis in the current−voltage characteristics. These properties, coupled with solution processability, make diF-TESADT attractive for electronic applications and demonstrate the technological potential of soluble oligomers. [ABSTRACT FROM AUTHOR]

Solution-processable small molecules have tremendous potential in macroelectronics applications by providing both high charge carrier mobility and low cost processing. Fluorinated 5,11-bis(triethylsilylethynl) anthradithiophene enables high performance thin film transistors due, in part, to a self-patterning process where crystals grow from chemically tailored contacts and bridge the transistor channel. This paper outlines a detailed microstructural study that identifies the crystallization mechanisms of the self-patterning. Two crystal habits are observed: we find that crystals on chemically modified electrodes predominantly form (001) oriented platelets while untreated surfaces form a fine mixture of (001) and (111) oriented crystals. For (001) oriented platelets, the (010) fast growth face lies in the plane of the film and allows extended growth from platelets nucleated on the electrode into the transistor channel. The in-plane charge carrier mobility of the (001) platelets is high; for short channel lengths, crystal growth fronts from adjacent electrodes bridge the channel gap, resulting in the excellent device performance. On untreated surfaces between devices, the low charge carrier mobility, finely mixed state provides self-isolation for stable device operation. [ABSTRACT FROM AUTHOR]

The carrier mobility of poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2- b]thiophene) semiconductors can be substantially enhanced after heating through a thermotropic mesophase transition, which causes a significant improvement in thin film structural order. By directly measuring film structure throughout a heating and cooling cycle, we identify the molecular origin of this mesophase transition as the melting of interdigitated linear alkane side chains, in this case quaterdecyl. The morphology and phase behavior throughout the thermal cycle are controlled by the changing conformation of the side chains. Surprisingly, the melting of the side chains allows increases in the backbone order, π−π stacking, and carrier mobility. Upon cooling, the side chains recrystallize to preserve the excellent mesophase order and enhanced electrical performance. [ABSTRACT FROM AUTHOR]