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The construction and control of 2D layered packing motifs with π-extended fused-ring molecules is of crucial importance for developing organic electronic materials and devices. Herein, we demonstrate that, when adequately substituted, two kinds of layered packing motifs are obtainable for benzo[1,2-b:4,5-b′]bis[b]benzothiophene (BBBT), which itself does not show layered crystallinity. We synthesized BBBT derivatives substituted with a combination of alkyl chains and a phenyl ring in a symmetric/asymmetric manner, 2,8-didecyl-BBBT (diC10-BBBT) and 2-decyl-8-phenyl-BBBT (Ph-BBBT-C10). We found that diC10-BBBT forms a layered π-stack (LπS) structure mainly composed of slipped parallel stacks, while Ph-BBBT-C10 forms a typical layered herringbone (LHB) packing structure chiefly composed of T-shaped contacts. This feature is associated with the non-layered packing motif in BBBT: typical π-stack and herringbone structures, both of whose polymorphs show a large slip along the molecular long axis. Calculations of intermolecular interaction energies between neighbouring molecules in the crystals reveal that the interchain interactions suppress the long-axis slip, leading to the formation of the LπS and the LHB, respectively. Both diC10-BBBT and Ph-BBBT-C10 form uniform (ultra)thin films originating from the layered crystallinity, and exhibit good transistor characteristics with a hole mobility of about 1 cm2 V−1 s−1. We discuss how the substituent modifications are useful as crystal engineering to explore the potential of π-extended molecules for electronic applications. [ABSTRACT FROM AUTHOR]

We have fabricated organic field-effect transistors (OFETs) with a highly oriented active layer of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2), which was formed with the help of a photoaligned polyimide film. Photoalignment is an attractive technique for integrating OFETs with aligned active layers on the same substrate, because of its potential capability of two-dimensional alignment patterning. The F8T2 layer formed on the photoaligned polyimide film showed an absorption dichroic ratio greater than 15 after annealing at 285 °C. Top-gate/bottom-contact-type OFETs with a parylene gate insulating layer exhibited an enhanced hole mobility (0.016 cm2 V-1 s-1) along the alignment direction of the F8T2 backbone structure and a suppressed one (0.002 cm2 V-1 s-1) along the perpendicular direction. This result shows that the photoaligned polyimide film is an attractive alignment layer for fabricating and integrating OFETs with aligned active layers. Current-direction-dependent bias stress effect was observed for those OFETs; when the current flowed parallel to the alignment direction of the F8T2 backbone structures, a larger negative threshold voltage shift was observed. This anisotropic bias stress effect was discussed on the basis of a microstructure model of aligned F8T2 films. [ABSTRACT FROM AUTHOR]

Delocalized singlet biradical hydrocarbons hold promise as new semiconducting materials for high-performance organic devices. However, to date biradical organic molecules have attracted little attention as a material for organic electronic devices. Here, this work shows that films of a crystallized diphenyl derivative of s-indacenodiphenalene (Ph2-IDPL) exhibit high ambipolar mobilities in organic field-effect transistors (OFETs). Furthermore, OFETs fabricated using Ph2-IDPL single crystals show high hole mobility ( μh = 7.2 × 10−1 cm2 V−1 s−1) comparable to that of amorphous Si. Additionally, high on/off ratios are achieved for Ph2-IDPL by inserting self-assembled mono­layer of alkanethiol between the semiconducting layer and the Au electrodes. These findings open a door to the application of ambipolar OFETs to organic electronics such as complementary metal oxide semiconductor logic circuits. [ABSTRACT FROM AUTHOR]

The authors have demonstrated the thin-film properties and the ambipolar transport of a delocalized singlet biradical hydrocarbon with two phenalenyl radical moieties (Ph2-IDPL). The organic field-effect transistors (OFETs) based on Ph2-IDPL exhibit ambipolar transport with balanced hole and electron mobilities in the order of 10-3 cm2/V s. The Ph2-IDPL film is an organic semiconductor with a low band gap of 0.8 eV and has small injection barriers from gold electrodes to both the highest occupied molecular orbital and the lowest unoccupied molecular orbital. A complementary metal-oxide-semiconductor-like inverter using two identical Ph2-IDPL based ambipolar OFETs shows a sharp inversion of the input voltage with high gain. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated self-assembled monolayer (SAM) treatment on SiO2 gate insulator of poly(3-hexylthiophene) (P3HT) thin-film transistor (TFT), and demonstrated a correlation between mobility and surface free energy of the insulator. The device with lower surface free energy shows higher mobility. The docosyltrichlorosilane (DCTS)-treated device exhibits the best performance among the various SAM-treated devices examined. Field-effect mobility, on/off ratio and threshold voltage of the DCTS-treated P3HT TFT were 0.015cm2/Vs, >105 and −14V, respectively. [Copyright &y& Elsevier]