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We demonstrate low-voltage, solution-processed organic transistors on rough plastic substrates with a carrier mobility over 0.2 cm2/V s, a turn-on voltage of near 0 V, and a record low subthreshold slope of ∼80 mV/decade in ambient conditions. These exceptional characteristics are attributed to (1) a device stacking architecture with a conducting polymeric gate and a double layered dielectric composed of low-temperature cross-linked poly(4-vinylphenol), (2) a low interface trap density achieved by modifying the dielectric surface with a phenyl-terminated self-assembled monolayer from 4-phenylbutyltrichlorosilane, and (3) controlled crystallization of a small-molecule organic semiconductor film with favorable charge transport microstructure and a low bulk trap density as deposited by an optimized solution-shearing process. The device performance under different operating voltages was also examined and discussed.

Single-crystal organic semiconductors have proven invaluable tools in the exploration of charge transport in molecular materials. We employ the elastomeric, photolithographically patterned single-crystal field-effect transistor in the study of an alpha-substituted oligothiophene. The terminal units specify a symmetric layered motif, while allowing the oligothiophene cores to pack closely. Angle-resolved measurements of the field-effect mobility reflect the symmetric edge/face interactions and isotropic mobility. These measurements are supported by electronic structure calculations that show nearly equivalent intermolecular interactions along cell diagonals. These results reveal that the transport is diffusive and a minimum of fourfold symmetry is required for in-plane mobility isotropy.

Organic single crystals have emerged as powerful tools for the exploration of the intrinsic charge transport properties of organic materials. To date, however, the limited number of fabrication techniques has forced a steep compromise between performance, reproducibility, range of feature sizes, gentle treatment of the single crystal, and facility of construction. Here the authors present a materials-general technique for the fabrication of single-crystal field-effect transistors with the use of a spin-coated elastomer gate dielectric and photolithographically defined source and drain electrodes. This allows the production of feature sizes and patterns previously impossible with reported elastomeric techniques yet yields devices with performance far superior to those fabricated on nonconformal dielectrics. The authors measure saturation-regime mobilities of 19.0 and 1.9cm2∕Vs for the semiconductors rubrene and pentacene, comparable to the best published values, and 2.4cm2∕Vs for tetracene, nearly double t...

Preliminary studies of the effect of x-ray irradiation, typically used to simulate radiation effects in space, on top contact, pentacene based field effect transistors have been carried out. Threshold voltage shifts in irradiated devices are consistent with positive charge trapping in the gate dielectric and a rebound effect is observed, independent of the sign of applied electric field during irradiation. Carrier mobility variations in positive electric field biased/irradiated devices are interpreted in terms of the effects of interface-state-like defects.