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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 top-contact FET and its change after thermal annealing.Characteristics of top-contact type FETs made using polycrystalline thin films of Ph-BTBT-10 fabricated from 0.5 wt% p-xylene solution in the SmE phase at ca., 80 °C. Output characteristics of FETs fabricated using the polycrystalline thin films (a) as-coated and (c) after thermal annealing at 120 °C for 5 min, (b) transfer characteristics of FETs fabricated with polycrystalline thin films both as-coated and after thermal annealing, (d) FET mobility as a function of annealing temperature, the error bars calculated from the standard deviations over 10 samples in each annealing temperature, (e) a topographic image of the polycrystalline thin films after annealing at 120 °C, as obtained by AFM, (f) out-of-plane small-angle XRD patterns for crystalline films as-coated and after annealing, with a schematic illustration of the crystalline structure and (g) DSC data for Ph-BTBT-10 during fast cooling and heating at 20 °C min−1.
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f3: Characteristics of top-contact FET and its change after thermal annealing.Characteristics of top-contact type FETs made using polycrystalline thin films of Ph-BTBT-10 fabricated from 0.5 wt% p-xylene solution in the SmE phase at ca., 80 °C. Output characteristics of FETs fabricated using the polycrystalline thin films (a) as-coated and (c) after thermal annealing at 120 °C for 5 min, (b) transfer characteristics of FETs fabricated with polycrystalline thin films both as-coated and after thermal annealing, (d) FET mobility as a function of annealing temperature, the error bars calculated from the standard deviations over 10 samples in each annealing temperature, (e) a topographic image of the polycrystalline thin films after annealing at 120 °C, as obtained by AFM, (f) out-of-plane small-angle XRD patterns for crystalline films as-coated and after annealing, with a schematic illustration of the crystalline structure and (g) DSC data for Ph-BTBT-10 during fast cooling and heating at 20 °C min−1.

Mentions: Bottom-gate and top-contact type FETs were fabricated with polycrystalline thin films of Ph-BTBT-10 on SiO2 (300 nm)/Si-substrates to allow the characterization of this compound as an OFET material. These FETs exhibited good p-channel performance, as summarized in Fig. 3a. Figure 3b demonstrates that the FET mobility under ambient condition was 2.1 cm2 V−1 s−1. Surprisingly, the FET transfer characteristics were significantly improved after brief thermal annealing at 120 °C for 5 min. Following this annealing, the drain current dramatically increased to 10−3 A and the FET mobility in the saturation region was also enhanced, reaching a value of 14.7 cm2 V−1 s−1, as shown in Fig. 3b,d.


Liquid crystals for organic thin-film transistors.

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

Characteristics of top-contact FET and its change after thermal annealing.Characteristics of top-contact type FETs made using polycrystalline thin films of Ph-BTBT-10 fabricated from 0.5 wt% p-xylene solution in the SmE phase at ca., 80 °C. Output characteristics of FETs fabricated using the polycrystalline thin films (a) as-coated and (c) after thermal annealing at 120 °C for 5 min, (b) transfer characteristics of FETs fabricated with polycrystalline thin films both as-coated and after thermal annealing, (d) FET mobility as a function of annealing temperature, the error bars calculated from the standard deviations over 10 samples in each annealing temperature, (e) a topographic image of the polycrystalline thin films after annealing at 120 °C, as obtained by AFM, (f) out-of-plane small-angle XRD patterns for crystalline films as-coated and after annealing, with a schematic illustration of the crystalline structure and (g) DSC data for Ph-BTBT-10 during fast cooling and heating at 20 °C min−1.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Characteristics of top-contact FET and its change after thermal annealing.Characteristics of top-contact type FETs made using polycrystalline thin films of Ph-BTBT-10 fabricated from 0.5 wt% p-xylene solution in the SmE phase at ca., 80 °C. Output characteristics of FETs fabricated using the polycrystalline thin films (a) as-coated and (c) after thermal annealing at 120 °C for 5 min, (b) transfer characteristics of FETs fabricated with polycrystalline thin films both as-coated and after thermal annealing, (d) FET mobility as a function of annealing temperature, the error bars calculated from the standard deviations over 10 samples in each annealing temperature, (e) a topographic image of the polycrystalline thin films after annealing at 120 °C, as obtained by AFM, (f) out-of-plane small-angle XRD patterns for crystalline films as-coated and after annealing, with a schematic illustration of the crystalline structure and (g) DSC data for Ph-BTBT-10 during fast cooling and heating at 20 °C min−1.
Mentions: Bottom-gate and top-contact type FETs were fabricated with polycrystalline thin films of Ph-BTBT-10 on SiO2 (300 nm)/Si-substrates to allow the characterization of this compound as an OFET material. These FETs exhibited good p-channel performance, as summarized in Fig. 3a. Figure 3b demonstrates that the FET mobility under ambient condition was 2.1 cm2 V−1 s−1. Surprisingly, the FET transfer characteristics were significantly improved after brief thermal annealing at 120 °C for 5 min. Following this annealing, the drain current dramatically increased to 10−3 A and the FET mobility in the saturation region was also enhanced, reaching a value of 14.7 cm2 V−1 s−1, as shown in Fig. 3b,d.

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.