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Grace Dansoa Tabi,Benjamin Nketia-Yawson,조제웅,노용영 한국고분자학회 2020 Macromolecular Research Vol.28 No.13
We report improved electron transport in solution-processed ambipolar organic field-effect transistors (OFETs) employing polymer dielectric blends of low-k poly(methyl methacrylate) (PMMA) and polyurethane (PU) elastomer. Ambipolar poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) OFETs typically showed an unbalanced hole and electron mobilities of 8.7 ± 0.4 × 10-4 and 2.0±0.1×10-4 cm2V-1s-1 respectively, using neat PMMA gate dielectric. By controlling the blending ratio of PU (0~50 v%) in the PMMA-PU blend dielectrics, we tuned the charge carrier transport in the F8BT OFETs. The electron mobility gradually increases significantly, resulting in nearly perfect ambipolar characteristics with hole and electron mobilities of 6.0 ±0.7× 10-4 and 9.7±0.4×10-4 cm2V-1s-1 respectively in PMMA: PU blend of 50:50 v%. The remarkable trend ensues from trapping of hole carriers at the dielectric/semiconductor by the -N-H- and carbonyl group (C=O) interface dipoles in the PU dielectric. The PMMA-PU blend dielectrics demonstrate excellent potentials for high-performance ambipolar OFETs, inverters, and complementary circuits.
Tabi, Grace Dansoa,Nketia-Yawson, Benjamin,Kang, So-Huei,Yang, Changduk,Noh, Yong-Young Elsevier 2018 ORGANIC ELECTRONICS Vol.54 No.-
<P><B>Abstract</B></P> <P>We report the evaluation of charge transport parameters of four p-type dichlorinated-2,1,3-benzothiadiazole (2ClBT) based conjugated polymers end-capped with different electron-donor units (thiophene (T), thieno[3,2-<I>b</I>]thiophene (TT), 2,2′-bithiophene (DT), and (E)-2-(2-(thiophen-2-yl)vinyl)thiophene (TVT)) in electrolyte gated organic field-effect transistors operating at a driving voltage of −2 V. Remarkable hole mobility improvement of 0.13–0.56 cm<SUP>2</SUP>V<SUP>−1</SUP>s<SUP>−1</SUP> were achieved in 2ClBTs based polymers, with P2ClBT-DT recording the highest mobility of 0.56 cm<SUP>2</SUP>V<SUP>−1</SUP>s<SUP>−1</SUP> and current on/off ratio ∼10<SUP>7</SUP>. Interestingly, a positive threshold voltage shift (Δ<I>V</I> <SUB>Th</SUB>) was observed in the transfer characteristics from the linear to saturation regime of all the 2ClBTs based polymer electrolyte gated OFET devices of <I>L</I> = 10 μm, contrary to devices with conventional poly(methyl methacrylate) gate dielectric, which showed a negative Δ<I>V</I> <SUB>Th</SUB> shift. Among the 2ClBTs based polymers, P2ClBT-TVT devices showed the lowest mobility and Δ<I>V</I> <SUB>Th</SUB> shift, which is attributed to severe ion diffusion in the polymer semiconducting layer owing to the vinyl group backbone susceptible to electrochemical doping. Our results emphasize essential selection consideration of the monomeric moieties, molecular ordering, π-π stacking and backbone planarity of conjugated polymers for electrolyte based organic devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We report high performance benzothiadiazole based OFETs with solid state ion dielectrics. </LI> <LI> Remarkable hole mobility improvement of 0.13–0.56 cm<SUP>2</SUP>V<SUP>−1</SUP>s<SUP>−1</SUP> were achieved. </LI> <LI> Structure-property relationship mainly is discussed by using different electron-donor units. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Chlorinated 2,1,3-Benzothiadiazole-Based Polymers for Organic Field-Effect Transistors
Kang, So-Huei,Tabi, Grace Dansoa,Lee, Junghoon,Kim, Gyoungsik,Noh, Yong-Young,Yang, Changduk American Chemical Society 2017 Macromolecules Vol.50 No.12
<P>The vital role of introducing chlorine (Cl) atoms onto conjugated polymers, which affects their semiconducting properties, is not yet well understood. A series of donoracceptor polymers based on dichlorinated-2,1,3-benzothiadiazole (2ClBT) and four different donor moieties with various conjugation lengths (thiophene (T), thieno[3,2-b]thiophene (TT), 2,2'-bithiophene (DT), and (E)-2-(2-(thiophen-2-yl)vinyl)thiophene (TVT)) were synthesized and used in organic field-effect transistors (OFETs). The structureproperty relationship associated with the 2ClBT-based polymers was thoroughly investigated via a range of techniques, and it was found that a change in the conjugation length of the main backbone could alter energy levels, morphology, and optoelectronic properties, which had a significant effect on the charge transport property. P2CLBT-TVT exhibited superior qualities relative to the other samples with respect to the degree of uniform film-forming ability and molecular organization and charge carrier transport, which resulted in the best hole mobility of 0.147 cm(2) V-1 s(1). Furthermore, we also emphasize that for all the polymers no substantial changes were observed in the OFET transfer-curve slopes during 200 testing cycles, indicating excellent operational stability. This study demonstrates that the design of semiconducting polymers possessing Cl atoms was effective at improving operating stability in the OFETs manufactured from them.</P>
Nketia-Yawson, Benjamin,Tabi, Grace Dansoa,Noh, Yong-Young American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.19
<P>We report on systematic mobility enhancements in electrolyte-gated organic field-effect transistors (OFETs) by thinning down the active layer and exploiting polymer solid-state electrolyte gate insulators (SEGIs). The SEGI is composed of homogeneous poly(vinylidene fluoride-<I>co</I>-hexafluoropropylene) [P(VDF-HFP)] polymer solution-ion gel blends of high areal capacitance of >10 μF cm<SUP>-2</SUP> at 1 Hz. By scaling up the poly(3-hexylthiophene) (P3HT) semiconducting layer by 1 order of magnitude (5-50 nm), an ultraviolet photoelectron spectroscopy examination reveals a downward vacuum-level shift generating a substantial hole injection barrier that originates from different interfacial dipole layer formations. The ultrathin (5.1 nm) P3HT FETs outperformed the other devices, exhibiting stable device characteristics with a highest field-effect mobility of >2 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP> (effective mobility of 0.83 ± 0.05 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>), on/off ratio of ∼10<SUP>6</SUP>, low threshold voltage of <−0.6 V, and low gate-leakage current levels of ∼10<SUP>5</SUP> below the on-current levels in 10 μm channel length devices. We observed a positive threshold voltage shift in the P3HT/SEGI FETs with decreasing semiconductor thickness. The aforementioned mobility is at least 10 times greater than that of neat P(VDF-HFP) devices. The significant FET performance is attributed to a better insulator/semiconductor interface, efficient hole injection from the Au electrode resulting in a low contact resistance of <500 Ω cm, and boosted charge-carrier densities in the transistor channel. This work demonstrates an excellent approach for carrier mobility enhancement and reliability assessment in low-voltage-operated electrolyte-gated OFETs.</P> [FIG OMISSION]</BR>
Nketia-Yawson, Benjamin,Jung, A-Ra,Noh, Yohan,Ryu, Gi-Seong,Tabi, Grace Dansoa,Lee, Kyung-Koo,Kim, BongSoo,Noh, Yong-Young American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.8
<P>Understanding the sensing mechanism in organic chemical sensors is essential for improving the sensing performance such as detection limit, sensitivity, and other response/recovery time, selectivity, and reversibility for real applications. Here, we report a highly sensitive printed ammonia (NH3) gas sensor based on organic thin film transistors (OTFTs) with fluorinated difluorobenzothiadiazole-dithienosilole polymer (PDFDT). These sensors detected NH3 down to 1 ppm with high sensitivity (up to 56%) using bar-coated ultrathin (<4 nm) PDFDT layers without using any receptor additives. The sensing mechanism was confirmed by cyclic voltammetry, hydrogen/fluorine nuclear magnetic resonance, and UV/visible absorption spectroscopy. PDFDT-NH3 interactions comprise hydrogen bonds and electrostatic interactions between the PDFDT polymer backbone and NH3 gas molecules, thus lowering the highest occupied molecular orbital levels, leading to hole trapping in the OTFT sensors. Additionally, density functional theory calculations show that gaseous NH3 molecules are captured via cooperation of fluorine atoms and dithienosilole units in PDFDT. We verified that incorporation of functional groups that interact with a specific gas molecule in a conjugated polymer is a promising strategy for producing high-performance printed OTFT gas sensors.</P>