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Published TCIMAIL newest issue No.200
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Organic Transistor Reagents: Soluble DNTT Precursors
Printed Electronics (PE) is an attractive technology for fabricating electronic circuits in a low-cost and efficient manner by printing. Flexible-sensor, -display, -solar cell and so on are possible to realize by printing these devices on flexible substrates such as plastic film or paper. High performance soluble organic semiconductors are required for the fabrication of circuits in PE.
Dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) developed by Takimiya is widely used as an air stable and high performance p-type organic semiconducting material. DNTT is insoluble in common organic solvents which makes fabrication of DNTT-based devices in a solution process difficult. To overcome this limitation, DNTT-PMIs [endo-DNTT-PMI (D5153) and exo-DNTT-PMI (D5154)] were developed.
DNTT-PMIs are convertible to DNTT by heating at 200 °C along with elimination of an N-phenylmaleimide (PMI) moiety. A DNTT thin film is successfully fabricated by coating DNTT-PMIs on a substrate followed by heating. As an actual application of DNTT-PMIs, fabrications of organic transistors and nonvolatile memories have been reported. Performances of organic field-effect transistors fabricated by using our products of DNTT-PMIs were evaluated under the cooperation of TEIJIN LIMITED, and found that each DNTT-PMI-based device showed high career mobilities (exo-DNTT-PMI: μmax = 2.33 cm2/Vs, endo-DNTT-PMI: μmax = 1.18 cm2/Vs).
Dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) developed by Takimiya is widely used as an air stable and high performance p-type organic semiconducting material. DNTT is insoluble in common organic solvents which makes fabrication of DNTT-based devices in a solution process difficult. To overcome this limitation, DNTT-PMIs [endo-DNTT-PMI (D5153) and exo-DNTT-PMI (D5154)] were developed.
DNTT-PMIs are convertible to DNTT by heating at 200 °C along with elimination of an N-phenylmaleimide (PMI) moiety. A DNTT thin film is successfully fabricated by coating DNTT-PMIs on a substrate followed by heating. As an actual application of DNTT-PMIs, fabrications of organic transistors and nonvolatile memories have been reported. Performances of organic field-effect transistors fabricated by using our products of DNTT-PMIs were evaluated under the cooperation of TEIJIN LIMITED, and found that each DNTT-PMI-based device showed high career mobilities (exo-DNTT-PMI: μmax = 2.33 cm2/Vs, endo-DNTT-PMI: μmax = 1.18 cm2/Vs).
Advantages
・Solution-processable DNTT precursors
・Thermally convertible to DNTT in thin-film
・Applicable to organic transistor and memory devices
・Thermally convertible to DNTT in thin-film
・Applicable to organic transistor and memory devices
Application
Solution processed OFETs using DNTT-PMIs
Ref. (a) J. Am. Chem. Soc., 2007, 129, 2224-2225. (b) Adv. Mater. 2015, 27, 727–732. (c) Adv. Mater. 2015, 27, 6606-6611. (d) Organic Electronics, 2013, 14, 1211–1217. (e) Appl. Phys. Express, 2015, 8, 101601-101604. (f) Y. Ikeda, T. Shiro, K. Takimiya, Patent JP5269825.
Device fabrication (endo-DNTT-PMI)
(1) Mix endo-DNTT-PMI (D5153) and polystyrene in 2:1 weight ratio
(2) Dissolve mixed powder in CHCl3 to prepare 1wt% solution
(3) Spin-coat*1 the solution onto cleaned- and UV/O3 treated-n+-Si/SiO2 substrate
(4) Anneal substrates at 200ºC for 10 min under air for converting the precursor to DNTT thin film
(5) Fabricate source and drain electrodes*2 by vacuum deposition of Au
*1 Spin-coating condition: 500rpm × 5s → 2000rpm × 20s
*2 channel length: 20μm or 200μm, channel width: 1000μm
(for exo-DNTT-PMI (D5154) based transistors, see Org. Electron. 2013, 14, 1211.)
Thin-film and OFET properties
Fig. 2 shows polarized optical microscopy (POM) image of DNTT thin film prepared from DNTT-PMI. Image clearly shows polycrystalline film morphology. As shown in Fig.3, fabricated devices show typical p-type characteristics.
Maximum carrier mobility 0.86 cm2/Vs was observed when channel length was 200µm. Carrier mobility was greatly improved to 2.33 cm2/Vs when the channel length was shortened to 20µm.
This high mobility can be assumed to be as following: the source and drain channels were completely filled in single grain, so the carrier transportation barrier caused by grain boundaries reduced.
Fig. 3 Transfer (left) and output (right) curves of OFET device prepared from endo-DNTT-PMI.
Table 1 Summary of OFET properties of DNTT prepared from endo-DNTT-PMI.