We developed a solution-processable, thin- and high dielectric polyurea (PU) gate insulator for low-voltage operation of organic thin-film transistors (TFTs). We synthesized solution-processed polyurea by precisely controlling hydrogen bonding through molecular design and molecular weight. A 60 nm-thick PU thin film exhibited high dielectric constant of 5.82 and excellent electrical insulating properties without the additional cross-linking process because of their strong intermolecular hydrogen bonding of urea groups. The hydrogen bonding of the polyurea was confirmed using Fourier transform infrared spectroscopy(FT-IR) and was quantitatively evaluated by measuring the interactive force using the atomic force microscopy(AFM). In addition, the effect of hydrogen bonding of polyurea on the insulating properties was systematically investigated through the combination of various monomers and the control of the thickness of the polyurea films. The 60 nm-thick polyurea was successfully fabricated through a solution process and showed a capacitance of 88 nF/cm2 and a leakage current of &lt;10-9 A/cm2 at 2 MV/cm. To investigate the potential of the PU thin film as a gate insulator, we fabricated dinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene (DNTT) organic thin-film transistors (OTFTs). The DNTT TFTs with the 60 nm-thick PU gate insulator showed excellent TFT performance with a field-effect mobility of 1.390 cm2/Vs and an on/off ratio of 5.84 × 105 at a low operation voltage below 3 V. The mobility of DNTT TFTs significantly improved with simple metal-oxide assisted surface treatment on PU gate insulator. In addition, polyurea thin film showed excellent solvent stability in various organic solvent for polymer organic semiconductor coating. We fabricated solution-processed poly[[2,5-bis(2-octyldodecyl)-2,3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1,4-diyl]-alt-[[2,2’-(2,5-thiophene)bis-thieno(3,2-b)thiophene]-5,5’-diyl]] (DPPT-TT) TFT on a 120 μm-thick flexible PET film as a substrate. These flexible TFT devices were successfully operated after 1000-times bending test at a bending radius of 3 mm and a bending speed of 5mm/s.

Solution-processable, thin and high dielectric polyurea gate insulator with strong hydrogen bonding for low-voltage operation of organic thin-film transistors

2019 Spring National Meeting

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