Improved thermal stability in organic FET fabricated with a soluble BTBT derivative

Iino, Hiroaki; Kobori, Takeo; Hanna, Jun‐ichi

doi:10.1016/j.jnoncrysol.2012.03.021

Cited by 60 publications

(37 citation statements)

References 17 publications

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“…2, there are parallel cracks in these films. It is interesting to note that similar cracks are reported in the films of liquid crystalline semiconductors prepared by spin-coating at elevated temperatures [23,24]. In Fig.…”

Section: Charactsupporting

confidence: 77%

Lateral solidification of a liquid crystalline semiconductor film induced by temperature gradient

et al. 2013

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Derivatives of [1]benzothieno[3,2-b]benzothiophene (BTBT) are attracting much attention as a highly soluble, highmobility semiconductor material for thin-film transistor applications. These small molecules are known to organize themselves into a single crystalline structure after spin coating or drop casting. Charge transport in a single crystal material is anisotropic in nature. Hence, it is desired to control its orientation during growth or recrystallization so that the source and drain electrodes of a transistor are to be placed along a faster transport direction. We propose to generate temperature gradient in a heated liquid crystalline thin film to induce lateral recrystallization. In experiment, we tried two methods. First, an aluminum plate with two narrow ridges was inserted between a temperature-controlled stage and a square silicon substrate with a 200nm-thick SiO 2 and a spin-coated C 8 -BTBT film. We raised the temperature of the stage to C 120 o and let it cool gradually. During cooling at around C 105 o , the color of the sample started to change, indicating a phase change. This change proceeded from the corners of the film and in about 30 seconds, darker regions merged at the center of the substrate. Second, the sample was placed at the edge of the stage. In this case, the color change started from the protruding corner of the sample and proceeded toward the other end. Micrograph observation revealed that cracks were formed in these films and they were perpendicular to the direction of the phase change.

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Section: Charactsupporting

confidence: 77%

Lateral solidification of a liquid crystalline semiconductor film induced by temperature gradient

et al. 2013

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“…The FET mobility values exhibit little change and remain above 10 cm 2 V −1 s −1 up to 140 °C, and a value of 2.6 cm 2 V −1 s −1 is obtained even after thermal stress is applied at 200 °C for 5 min. In contrast, the mobility in FETs fabricated with polycrystalline thin films of 2,7-didecylbenzothienobenzothiophene (10-BTBT-10) abruptly decreases after thermal stress is applied above 100 °C, at which temperature the crystal film was observed to melt into droplets due to the phase transition to a liquid-like, less-ordered phase of SmA and the FETs ceased to function 25 26 .…”

Section: Resultsmentioning

confidence: 99%

Liquid crystals for organic thin-film transistors

2015

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Crystalline thin films of organic semiconductors are a good candidate for field effect transistor (FET) materials in printed electronics. However, there are currently two main problems, which are associated with inhomogeneity and poor thermal durability of these films. Here we report that liquid crystalline materials exhibiting a highly ordered liquid crystal phase of smectic E (SmE) can solve both these problems. We design a SmE liquid crystalline material, 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10), for FETs and synthesize it. This material provides uniform and molecularly flat polycrystalline thin films reproducibly when SmE precursor thin films are crystallized, and also exhibits high durability of films up to 200 °C. In addition, the mobility of FETs is dramatically enhanced by about one order of magnitude (over 10 cm2 V−1 s−1) after thermal annealing at 120 °C in bottom-gate-bottom-contact FETs. We anticipate the use of SmE liquid crystals in solution-processed FETs may help overcome upcoming difficulties with novel technologies for printed electronics.

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“…The FET fabricated with 8-Tp-BTBT can be operated well even after undergoing thermal stress at 150°C for 5 min, whereas the FET from C 10 -BTBT is substantially degraded because the C 10 -BTBT is melted, as shown in Figure 6b. 34,35 A novel smectic liquid crystalline OFET material, Ph-BTBT-10 Taking account of the advantages of highly ordered smectic liquid crystals for OFET materials discussed in the previous sections, Ph-BTBT-10 was designed and synthesized to demonstrate its high potential as a soluble OFET material, as shown in Figure 7a. Ph-BTBT-10 shows a narrow solubility of 2 g l − 1 in toluene at 20°C for solution processes and exhibits a SmE phase from 142 to 210°C in the heating process and from 210 to 98°C in the cooling process.…”

Section: Liquid Crystalline Semiconductors For Ofets H Iino and J Hannamentioning

confidence: 99%

Liquid crystalline organic semiconductors for organic transistor applications

Iino

Hanna

2016

Polym J

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The recent development of materials for organic field effect transistors (OFETs), including small-molecule and polymer materials, are briefly reviewed, and the problems that remain to be solved prior to practical application and use are discussed. Liquid crystalline materials are good candidates for OFETs because of their advantageous properties over soluble small-molecule materials. Liquid crystalline materials show good solution processability for the fabrication of uniform crystalline thin films using the precursor of uniform liquid crystalline thin films. In addition, liquid crystalline materials having their highly ordered liquid crystal phases show a high thermal durability despite their high solubility. The novel liquid crystalline material 2-phenyl-7-decyl [1]benzothieno [3,2-b][1]benzothiophene exhibits a highly ordered liquid crystal phase, the Smectic E (SmE) phase, which has good solution processability for uniform crystalline thin films by the precursor of uniform SmE thin films, shows high thermal durability and solubility, and can be used for transistor devices having a high mobility, over 10 cm 2 Vs − 1 , by thermal annealing at 120°C for 5 min. Thus, liquid crystalline materials are good semiconductor materials for organic transistor applications instead of polymer materials. INTRODUCTIONMaterials for organic field effect transistors (OFETs) have attracted considerable attention since their high mobility of over 1 cm 2 Vs − 1 , comparable to that of amorphous silicon FETs, was reported in polycrystalline thin films of pentacene fabricated by vacuum evaporation. 1 OFETs are very attractive for device applications because they can be fabricated even at room temperature to create flexible electronics on plastic substrates. Recent materials research for OFETs has been focused on soluble OFET materials because of their device applications in printed electronics. In this review, the recent development of OFET materials is briefly discussed, including the use of small molecules and polymers, and the remaining problems to be solved for their practical applications are discussed. Then, a new candidate for OFET materials, that is, liquid crystals, as a self-organizing molecular semiconductor, is discussed, focusing on how liquid crystallinity can solve the existing problems, and its high potential for OFET applications is demonstrated with a highly ordered smectic liquid crystal of 2-phenyl-7-decyl[1]benzothieno [3,2-b][1] benzothiophene (Ph-BTBT-10). 2

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Improved thermal stability in organic FET fabricated with a soluble BTBT derivative

Cited by 60 publications

References 17 publications

Lateral solidification of a liquid crystalline semiconductor film induced by temperature gradient

Lateral solidification of a liquid crystalline semiconductor film induced by temperature gradient

Liquid crystals for organic thin-film transistors

Liquid crystalline organic semiconductors for organic transistor applications

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