Tuning the Work Function of Printed Polymer Electrodes by Introducing a Fluorinated Polymer To Enhance the Operational Stability in Bottom-Contact Organic Field-Effect Transistors

Kim, Se Hyun,Kim, Jiye,Nam, Sooji,Lee, Hwa Sung,Lee, Seung Woo,Jang, Jaeyoung American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.14

<P>Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) is a promising electrode material for organic electronic devices due to its high conductivity, good mechanical flexibility, and feasibility of easy patterning with various printing methods. The work function of PEDOT:PSS needs to be increased for efficient hole injection, and the addition of a fluorine-containing material has been reported to increase the work function of PEDOT:PSS. However, it remains a challenge to print PEDOT:PSS electrodes while simultaneously tuning their work functions. Here, we report work function tunable PEDOT:PSS/Nafion source/drain electrodes formed by electrohydrodynamic printing technique with PEDOT:PSS/Nafion mixture solutions for highly stable bottom contact organic field-effect transistors (OFETs). The surface properties and work function of the printed electrode can be controlled by varying the Nafion ratio, due to the vertical phase separation of the PEDOT:PSS/ Nafion. The PEDOT:PSS/Nafion electrodes exhibit a low hole injection barrier, which leads to efficient charge carrier injection from the electrode to the semiconductor. As a result, pentacene-based OFETs with PEDOT:PSS/Nafion electrodes show increased charge carrier mobilities of 0.39 cm(2)/(V.s) compared to those of devices with neat PEDOT:PSS electrodes (0.021 cm(2)/(V.s)). Moreover, the gate-bias stress stability of the OFETs is remarkably improved by employing PEDOT:PSS/Nafion electrodes, as demonstrated by a reduction of the threshold voltage shift from -1.84 V to -0.28 V.</P>

Highly-impermeable Al₂O₃/HfO₂ moisture barrier films grown by low-temperature plasma-enhanced atomic layer deposition

Kim, Lae Ho,Jang, Jin Hyuk,Jeong, Yong Jin,Kim, Kyunghun,Baek, Yonghwa,Kwon, Hyeok-jin,An, Tae Kyu,Nam, Sooji,Kim, Se Hyun,Jang, Jaeyoung,Park, Chan Eon Elsevier 2017 Organic Electronics Vol.50 No.-

<P><B>Abstract</B></P> <P>Polymer substrates are essential components of flexible electronic applications such as OTFTs, OPVs, and OLEDs. However, high water vapor permeability of polymer films can significantly reduce the lifetime of flexible electronic devices. In this study, we examined the water vapor permeation barrier properties of Al<SUB>2</SUB>O<SUB>3</SUB>/HfO<SUB>2</SUB> mixed oxide films on polymer substrates. Al<SUB>2</SUB>O<SUB>3</SUB>/HfO<SUB>2</SUB> films deposited by plasma-enhanced atomic layer deposition were transparent, chemically stable in water and densely amorphous. At 60 °C and 90% relative humidity (RH) accelerated condition, 50-nm-thick Al<SUB>2</SUB>O<SUB>3</SUB>/HfO<SUB>2</SUB> had water vapor transmission rate (WVTR) = 1.44 × 10<SUP>−4</SUP> g m<SUP>−2</SUP> d<SUP>−1</SUP>, whereas single layers of Al<SUB>2</SUB>O<SUB>3</SUB> had WVTR = 3.26 × 10<SUP>−4</SUP> g m<SUP>−2</SUP> d<SUP>−1</SUP> and of HfO<SUB>2</SUB> had WVTR = 6.75 × 10<SUP>−2</SUP> g m<SUP>−2</SUP> d<SUP>−1</SUP>. At 25 °C and 40% RH, 50-nm-thick Al<SUB>2</SUB>O<SUB>3</SUB>/HfO<SUB>2</SUB> film had WVTR = 2.63 × 10<SUP>−6</SUP> g m<SUP>−2</SUP> d<SUP>−1</SUP>, which is comparable to WVTR of conventional glass encapsulation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Al<SUB>2</SUB>O<SUB>3</SUB>, HfO<SUB>2</SUB>, and Al<SUB>2</SUB>O<SUB>3</SUB>/HfO<SUB>2</SUB> mixed oxide films were deposited by plasma-enhanced atomic layer deposition (PEALD). </LI> <LI> Al<SUB>2</SUB>O<SUB>3</SUB>/HfO<SUB>2</SUB> mixed oxide films were prepared by alternating deposition of Al<SUB>2</SUB>O<SUB>3</SUB> and HfO<SUB>2</SUB> (one layer of each per cycle). </LI> <LI> Al<SUB>2</SUB>O<SUB>3</SUB>/HfO<SUB>2</SUB> mixed oxide films had densely-packed amorphous structure due to Al<SUB>2</SUB>O<SUB>3</SUB> and high chemical stability due to HfO<SUB>2</SUB>. </LI> <LI> All Al<SUB>2</SUB>O<SUB>3</SUB>/HfO<SUB>2</SUB> mixed oxide films were less permeable to moisture than were single Al<SUB>2</SUB>O<SUB>3</SUB> or HfO<SUB>2</SUB> films. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

A composite of a graphene oxide derivative as a novel sensing layer in an organic field-effect transistor

Kim, Yebyeol,An, Tae Kyu,Kim, Jiye,Hwang, Jihun,Park, Seonuk,Nam, Sooji,Cha, Hyojung,Park, Won Jeong,Baik, Jeong Min,Park, Chan Eon The Royal Society of Chemistry 2014 Journal of Materials Chemistry C Vol.2 No.23

<▼1><P>The receptor material (OA-GO)/polymeric semiconductor (F8T2) structure is newly introduced to active layer of OFET gas sensors and demonstrated to have better sensing ability than a comparable device with a polymer-only active layer.</P></▼1><▼2><P>We report the fabrication of a gas sensor with an oleylamine-modified graphene oxide (OA-GO)/poly(9-9′-dioctyl-fluorene-<I>co</I>-bithiophene) (F8T2) composite as an active layer and demonstrate that it has better sensing ability than a comparable device with an F8T2-only active layer. OA-GO was chosen as the receptor material because of its enhanced interaction with gas analytes and its easy mixing with F8T2. OA-GO was synthesized by a simple condensation reaction between GO and oleylamine (9-octadecylamine), and characterized by Fourier transform infrared spectroscopy. The sensitivities of the gas sensors with respect to acetone and ethanol analytes were investigated by measuring the electrical parameters of the corresponding organic field effect transistor at room temperature. The sensitivity of the OA-GO/F8T2 composite device was up to 34 times that of the F8T2 device for the mobility change of acetone.</P></▼2>

Feminist Critics on transformation of Recent Korean Family context

Kim Woojong,Kim Jeongmin,Chang Sooji 이화여자대학교 아시아여성학센터 2005 이화여자대학교 아시아여성학센터 학술대회자료집 Vol.2005 No.6

Different Paths to Citizenship Development of Korean College Students by Academic Discipline

Sooji Kim,Byung Shik Rhee 한국교육학회 2016 敎育學硏究 Vol.54 No.1

This study was prompted by a consciousness of the need for today’s younger generations’ enhanced citizenship. Underlying assumptions are that higher education is essentially responsible for nurturing civic minds of the young and furthermore, that it is unquestionably capable of achieving this goal. In this regard, this research delved into college involvement predictors vital to students’ citizenship development and additionally, looked for different paths to development across academic disciplines. A stratified random sample of 5,093 juniors and seniors at 51 four-year Korean universities, was analyzed using hierarchical linear modeling (HLM 6.08). The findings indicated that students in Social Sciences reported the most development in citizenship during college, compared with those in Arts and Humanities, Business, Sciences, Engineering, and Professional fields. Another conclusive discovery was that ‘academic interaction with peers’ and ‘sense of belonging’ had positive effects on students’ citizenship development in all academic disciplines. Other college involvement predictors, however, had varying influences on students according to their affiliated academic disciplines. Finally, psychological factors such as sense of belonging had stronger impacts on students’ citizenship development than college involvement predictors in all academic fields except Business.

Investment timing decisions in hydropower adaptation projects using climate scenarios: A case study of South Korea

Kim, Kyeongseok,Jeong, Hoyoung,Ha, Sooji,Bang, Seongdeok,Bae, Deg-Hyo,Kim, Hyoungkwan Elsevier 2017 Journal of cleaner production Vol.142 No.4

<P><B>Abstract</B></P> <P>Climate change alters the energy production of existing hydropower plants. Old-established facilities of hydropower are insufficient to handle changes in runoff under climate change. These facilities should be retrofitted and adapted to climate change. Adaptation of hydropower to climate change has two purposes: first, to fully utilize future water resources for maximizing electricity generation; and second, to generate profits in return of investment costs. Investment in the adaptation depends on issues such as climate scenarios, investment costs, and timing of implementation. Since future climate scenarios are intrinsically time-dependent, investment timing is the biggest issue. We propose the Adaptive Investment Model (AIM) to determine the timing of investment, using real options valuation. AIM comprises four steps: identification of hydropower adaptation to climate change (step 1), calculation of key variables (step 2), real options valuation (ROV) (step 3), and decision-making (step 4). This model allows investors to assess the economic feasibility and suggests optimal investment timing for adaptation to climate change. A case study involving the Chuncheon hydropower plant in South Korea demonstrated that AIM could generate an effective adaptation strategy.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The timing of adaptation investment in hydropower plant was explored. </LI> <LI> Wise strategy for hydropower adaptation correlates with investment timing. </LI> <LI> The Adaptive Investment Model determines investment timing using climate scenarios. </LI> <LI> The economic impacts of climate change on hydropower were analyzed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Multilayer Transfer Printing for Pixelated, Multicolor Quantum Dot Light-Emitting Diodes

Kim, Bong Hoon,Nam, Sooji,Oh, Nuri,Cho, Seong-Yong,Yu, Ki Jun,Lee, Chi Hwan,Zhang, Jieqian,Deshpande, Kishori,Trefonas, Peter,Kim, Jae-Hwan,Lee, Jungyup,Shin, Jae Ho,Yu, Yongjoon,Lim, Jong Bin,Won, Sa American Chemical Society 2016 ACS NANO Vol.10 No.5

<P>Here, we report multilayer stacking of films of quantum dots (QDs) for the purpose of tailoring the energy band alignment between charge transport layers and light emitting layers of different color in quantum dot light emitting diodes (QD LED) for maximum efficiency in full color operation. The performance of QD LEDs formed by transfer printing compares favorably to that of conventional devices fabricated by spin-casting. Results indicate that zinc oxide (ZnO) and titanium dioxide (TiO2) can serve effectively as electron transport layers (ETLs) for red and green/blue QD LEDs, respectively. Optimized selections for each QD layer can be assembled at high yields by transfer printing with sacrificial fluoropolymer thin films to provide low energy surfaces for release, thereby allowing shared common layers for hole injection (HIL) and hole transport (HTL), along with customized ETLs. This strategy allows cointegration of devices with heterogeneous energy band diagrams, in a parallelized scheme that offers potential for high throughput and practical use.</P>

Optimization of Al₂O₃/TiO₂ nanolaminate thin films prepared with different oxide ratios, for use in organic light-emitting diode encapsulation, <i>via</i> plasma-enhanced atomic layer deposition

Kim, Lae Ho,Jeong, Yong Jin,An, Tae Kyu,Park, Seonuk,Jang, Jin Hyuk,Nam, Sooji,Jang, Jaeyoung,Kim, Se Hyun,Park, Chan Eon Royal Society of Chemistry 2016 Physical Chemistry Chemical Physics Vol. No.

<P>Encapsulation is essential for protecting the air-sensitive components of organic light-emitting diodes (OLEDs), such as the active layers and cathode electrodes. Thin film encapsulation approaches based on an oxide layer are suitable for flexible electronics, including OLEDs, because they provide mechanical flexibility, the layers are thin, and they are easy to prepare. This study examined the effects of the oxide ratio on the water permeation barrier properties of Al2O3/TiO2 nanolaminate films prepared by plasma-enhanced atomic layer deposition. We found that the Al2O3/TiO2 nanolaminate film exhibited optimal properties for a 1 : 1 atomic ratio of Al2O3/TiO2 with the lowest water vapor transmission rate of 9.16 x 10(-5) g m(-2) day(-1) at 60 degrees C and 90% RH. OLED devices that incorporated Al2O3/TiO2 nanolaminate films prepared with a 1 : 1 atomic ratio showed the longest shelf-life, in excess of 2000 hours under 60 degrees C and 90% RH conditions, without forming dark spots or displaying edge shrinkage.</P>

A study on cobalt substitution in sodium manganese mixed-anion phosphates as positive electrode materials for Na-ion batteries

Ryu, Soojy,Wang, Ji Eun,Kim, Joo-Hyung,Ruffo, Riccardo,Jung, Young Hwa,Kim, Do Kyung Elsevier 2019 Journal of Power Sources Vol.444 No.-

<P><B>Abstract</B></P> <P>Sodium polyanionic materials provide various structural frameworks compared to their lithium counterparts, leading to diverse studies on novel polyanion-based electrode materials for sodium ion batteries. Na<SUB>4</SUB>M<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB>P<SUB>2</SUB>O<SUB>7</SUB> (M = Mn, Fe, Co, Ni, and Mg) is a new class of mixed-anion phosphates combined with two polyanion groups, (PO<SUB>4</SUB>)<SUP>3−</SUP> and (P<SUB>2</SUB>O<SUB>7</SUB>)<SUP>4−</SUP>. It is an attractive electrode candidate because of its stable cyclability and low volume changes upon cycling. Although Mn-based mixed-anion phosphate materials have shown a high redox potential of 3.8 V vs. Na<SUP>+</SUP>/Na, they have suffered from low electrical conductivity and structural distortion upon oxidation. Partial substitution of Mn by other divalent cations is an efficient strategy to suppress lattice distortion and to affect the phase transition process during electrochemical cycling. Here we study the cation substitution effect of the Mn-based mixed-anion phosphates on the phase stability and the kinetics of the electrochemical reaction. The electrochemical reversibility was found to be improved by certain cation substitution. In particular, Co substitution not only increased the operating voltage but also enhanced both cyclability and rate capability. Furthermore, we investigate the phase changes upon cycling using <I>in situ</I> synchrotron X-ray diffraction, supporting the positive effect of the mixed-anion phosphate structure through cation substitution.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Co substitution on Mn-based mixed-anion phosphate by solution combustion synthesis. </LI> <LI> Substituted Co alleviated structure distortion and lowered phase transition barrier. </LI> <LI> Enhanced operating potential and half-cell performance of mixed-anion phosphate. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

High-Performance Low-VoltageOrganic Field-EffectTransistors Prepared on Electro-Polished Aluminum Wires

Nam, Sooji,Jang, Jaeyoung,Park, Jong-Jin,Kim, Sang Won,Park, Chan Eon,Kim, Jong Min AmericanChemical Society 2012 ACS APPLIED MATERIALS & INTERFACES Vol.4 No.1

<P>We report the preparation of high-performance low-voltagepentacene-basedorganic field-effect transistors (OFETs) fabricated on a metallicfiber (Al wire) substrate. The surface roughness of the wire was significantlyreduced after 10 min of electro-polishing. A 120 nm thick Al<SUB>2</SUB>O<SUB>3</SUB> gate dielectric layer was deposited on the anodizedwire, followed by octadecyltrichlorosilane (ODTS) treatment. The ODTS-modifiedAl<SUB>2</SUB>O<SUB>3</SUB> gate dielectrics formed around the Alwire showed a high capacitance of 50.1 nF cm<SUP>–2</SUP> andhydrophobic surface characteristics. The resulting OFETs exhibitedhysteresis-free operation with a high mobility of 0.345 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP> within a low operatingvoltage range of −5 V, and maintained their high performanceat an applied tensile strain of bending radius ∼2.2.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2012/aamick.2012.4.issue-1/am2011405/production/images/medium/am-2011-011405_0002.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am2011405'>ACS Electronic Supporting Info</A></P>