Large area liquid crystal monodomain field-effect transistors
article
Butyl, hexyl, and decyl derivatives of the liquid-crystalline organic semiconductor 5,5″-bis(5-alkyl-2-thienylethynyl)-2,2′:5′, 2″-terthiophene were synthesized and studied with respect to their structural, optical, and electrical properties. By means of an optimized thermal annealing scheme the hexyl and decyl compounds could be processed into self-assembled monodomain films of up to 150 mm in diameter. These were investigated with X-ray diffractometry, which revealed a clearly single-crystalline monoclinic morphology with lamellae parallel to the substrate. Within the lamellae the molecules were found to arrange with a tilt of about 50° with the rubbing direction of the polyimide alignment layer. The resulting, close side-to-side packing was confirmed by measurements of the UV/vis absorption, which showed a dichroic ratio of 19 and indicated H-aggregation. AFM analyses revealed self-affinity in the surface roughness of the monodomain. The compounds showed bipolar charge transport in TOF measurements, with hole mobilities reaching up to 0.02 cm2/Vs and maximum electron mobilities around 0.002 cm2/Vs. The hexyl derivative was processed into large-area monodomain top-gate field-effect transistors, which were stable for months and showed anisotropic hole mobilities of up to 0.02 cm2/Vs. Compared to multidomain bottom-gate transistors the monodomain formation allowed for a mobility increase by 1 order of magnitude.
Topics
AnnealingCrystalline materialsLiquid crystal displaysSemiconducting organic compoundsSynthesis (chemical)X ray diffractionAnisotropic hole mobilitiesSelf-affinitySingle-crystalline monoclinic morphologyUV/vis absorptionField effect transistorsPolyimideThiophene derivativeAtomic force microscopyLight absorptionLiquid crystalSemiconductorSurface property
TNO Identifier
239133
ISSN
0002-7863
Source
Journal of the American Chemical Society, 128(7), pp. 2336-2345.
Publisher
American Chemical Society ACS
Pages
2336-2345
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