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Liquid crystals for organic thin-film transistors.

Iino H, Usui T, Hanna J - Nat Commun (2015)

Bottom Line: 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.In addition, the mobility of FETs is dramatically enhanced by about one order of magnitude (over 10 cm(2) V(-1) s(-1)) after thermal annealing at 120 °C in bottom-gate-bottom-contact FETs.

View Article: PubMed Central - PubMed

Affiliation: 1] Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, J1-2, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan [2] Japan Science and Technology Agency (JST), Core Research for Evolutional Science and Technology (CREST), 4-1-8 Hon-cho, Kawaguchi 332-0012, Japan.

ABSTRACT
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 cm(2) 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.

No MeSH data available.


Characteristics of polycrystalline thin films of Ph-BTBT-10.The polycrystalline thin film were fabricated from a 0.5 wt% diethylbenzene solution at ∼110 °C, (a,d) texture as determined by optical microscopy and (b,e) AFM images. Insets show cross-sectional profiles observed by (a,d) confocal laser scanning microcopy and (b,e) AFM. (a,b) As-coated polycrystalline film and (d,e) after thermal stress at 150 °C for 5 min. (a,d) White bars indicate scale of 20 μm in length. (c) Four d-spacings of Ph-BTBT-10 in crystal and SmE phase in wide- and small-angle regions as a function of temperature.
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f2: Characteristics of polycrystalline thin films of Ph-BTBT-10.The polycrystalline thin film were fabricated from a 0.5 wt% diethylbenzene solution at ∼110 °C, (a,d) texture as determined by optical microscopy and (b,e) AFM images. Insets show cross-sectional profiles observed by (a,d) confocal laser scanning microcopy and (b,e) AFM. (a,b) As-coated polycrystalline film and (d,e) after thermal stress at 150 °C for 5 min. (a,d) White bars indicate scale of 20 μm in length. (c) Four d-spacings of Ph-BTBT-10 in crystal and SmE phase in wide- and small-angle regions as a function of temperature.

Mentions: Ph-BTBT-10 polycrystalline thin films were fabricated by spin coating a diethylbenzene solution at the SmE phase temperature of 110 °C and cooling the SmE films to room temperature. The resulting polycrystalline films were very uniform, which are very similar to those fabricated from less-ordered liquid crystalline films previously reported1920, but contained no cracks and maintained the crystal state up to 143 °C. The different colors in the film shown in Fig. 2a are due to interference in the samples consisting of a Ph-BTBT-10 layer of about 50 nm and silicon dioxide of 300 nm on Si-substrate, indicating that the film has a small variation in thickness within a film. The absence of cracks in the polycrystalline thin films is attributed to similar thermal expansion coefficients of lattices within the molecular layer in the SmE and crystal films, which was confirmed by continuous decrease of three d-spacings corresponding to SmE structure as a function of temperature structure, in spite of the phase transition from SmE to crystal phases, as shown in Fig. 2c and Supplementary Fig. 2. These films are therefore very different from the cracked polycrystalline thin films previously fabricated from SmA films of a dialkyl-BTBT derivative20. Atomic force microscope (AFM) image of the polycrystalline thin film shows wide terrace structures with steps of ∼2.8 nm, as shown in Fig. 2b, corresponding to the molecular length along the long molecular axis of Ph-BTBT-10 as shown in Supplementary Fig. 3. This indicates that the Ph-BTBT-10 molecules are aligned perpendicular to the substrate. Thanks to the solid-like SmE phase similar to crystal phase, the resulting films not only maintained the film shape but also molecular flatness even after heating at 150 °C for 5 min, as shown in Fig. 2d,e.


Liquid crystals for organic thin-film transistors.

Iino H, Usui T, Hanna J - Nat Commun (2015)

Characteristics of polycrystalline thin films of Ph-BTBT-10.The polycrystalline thin film were fabricated from a 0.5 wt% diethylbenzene solution at ∼110 °C, (a,d) texture as determined by optical microscopy and (b,e) AFM images. Insets show cross-sectional profiles observed by (a,d) confocal laser scanning microcopy and (b,e) AFM. (a,b) As-coated polycrystalline film and (d,e) after thermal stress at 150 °C for 5 min. (a,d) White bars indicate scale of 20 μm in length. (c) Four d-spacings of Ph-BTBT-10 in crystal and SmE phase in wide- and small-angle regions as a function of temperature.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4403349&req=5

f2: Characteristics of polycrystalline thin films of Ph-BTBT-10.The polycrystalline thin film were fabricated from a 0.5 wt% diethylbenzene solution at ∼110 °C, (a,d) texture as determined by optical microscopy and (b,e) AFM images. Insets show cross-sectional profiles observed by (a,d) confocal laser scanning microcopy and (b,e) AFM. (a,b) As-coated polycrystalline film and (d,e) after thermal stress at 150 °C for 5 min. (a,d) White bars indicate scale of 20 μm in length. (c) Four d-spacings of Ph-BTBT-10 in crystal and SmE phase in wide- and small-angle regions as a function of temperature.
Mentions: Ph-BTBT-10 polycrystalline thin films were fabricated by spin coating a diethylbenzene solution at the SmE phase temperature of 110 °C and cooling the SmE films to room temperature. The resulting polycrystalline films were very uniform, which are very similar to those fabricated from less-ordered liquid crystalline films previously reported1920, but contained no cracks and maintained the crystal state up to 143 °C. The different colors in the film shown in Fig. 2a are due to interference in the samples consisting of a Ph-BTBT-10 layer of about 50 nm and silicon dioxide of 300 nm on Si-substrate, indicating that the film has a small variation in thickness within a film. The absence of cracks in the polycrystalline thin films is attributed to similar thermal expansion coefficients of lattices within the molecular layer in the SmE and crystal films, which was confirmed by continuous decrease of three d-spacings corresponding to SmE structure as a function of temperature structure, in spite of the phase transition from SmE to crystal phases, as shown in Fig. 2c and Supplementary Fig. 2. These films are therefore very different from the cracked polycrystalline thin films previously fabricated from SmA films of a dialkyl-BTBT derivative20. Atomic force microscope (AFM) image of the polycrystalline thin film shows wide terrace structures with steps of ∼2.8 nm, as shown in Fig. 2b, corresponding to the molecular length along the long molecular axis of Ph-BTBT-10 as shown in Supplementary Fig. 3. This indicates that the Ph-BTBT-10 molecules are aligned perpendicular to the substrate. Thanks to the solid-like SmE phase similar to crystal phase, the resulting films not only maintained the film shape but also molecular flatness even after heating at 150 °C for 5 min, as shown in Fig. 2d,e.

Bottom Line: 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.In addition, the mobility of FETs is dramatically enhanced by about one order of magnitude (over 10 cm(2) V(-1) s(-1)) after thermal annealing at 120 °C in bottom-gate-bottom-contact FETs.

View Article: PubMed Central - PubMed

Affiliation: 1] Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, J1-2, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan [2] Japan Science and Technology Agency (JST), Core Research for Evolutional Science and Technology (CREST), 4-1-8 Hon-cho, Kawaguchi 332-0012, Japan.

ABSTRACT
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 cm(2) 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.

No MeSH data available.