Single crystal structure and electroluminescence efficiency of blue fluorescence OLED emitters using triple core chromophores

Jung, Hyocheol,Kang, Seokwoo,Sim, Yeonhee,Jung, Mina,Wakamiya, Atsushi,Lee, Ji-Hoon,Park, Jongwook Elsevier 2019 Organic electronics Vol.73 No.-

<P><B>Abstract</B></P> <P>The relationship between the single crystal structure of materials and the EL performance of doped OLED devices was investigated. The 1,6-bis-(10-[1,1′;3′,1″]terphenyl-5′-yl-anthracen-9-yl)-pyrene (1,6 DAP-TP) has a dihedral angle (α) of 78.4° and a dihedral angle (β) of 81.2°, a relatively more twisted single crystal structure compared to that of 6,12-bis-(10-[1,1′;3′,1″]terphenyl-5′-yl-anthracen-9-yl)-chrysene (DAC-TP). Such a highly twisted molecular structure can improve the electroluminescence (EL) efficiency of a material because it can inhibit rotational and vibrational motions. Also, since the doped state and single crystal structure imply, respectively, a diluted state and a molecular state, the EL efficiency of the doped OLED device is related to single crystal structure. In a 4% doped OLED device, 1,6 DAP-TP and DAC-TP showed CE of 2.10 cd A<SUP>−1</SUP> and 0.93 cd A<SUP>−1</SUP>, respectively. With its relatively more twisted single crystal structure, 1,6 DAP-TP showed higher CE in a doped OLED device than DAC-TP. Both compounds had ultra-deep blue emission y values of 0.06 or less for the color coordinates, which satisfy high density television display requirements (y value less than 0.08).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Relationship between the single crystal structure of materials and the EL performance of doped OLED devices was investigated. </LI> <LI> Highly twisted molecular structure can improve the EL efficiency of a material because it can inhibit various transition. </LI> <LI> As a result, doped OLED device using 1,6 DAP-TP had a CE of 2.10 cd A<SUP>−1</SUP>, 4.24% EQE, and CIE (x, y) (0.16, 0.06). </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Synthesis and Physical Properties of New Pyrene Derivative with Bulky Side Groups for Blue Emission

Jung, Mina,Lee, Jaehyun,Jung, Hyocheol,Park, Jongwook American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.8

<P>Organic light-emitting diodes (OLEDs) have attracted much attention from academia and industry field because of their various applications such as large area flat-panel displays and lightings. We designed and synthesized new pyrene derivative with 1,6-bis(3',5'-diphenylbiphenyl-4-yl)pyrene (1,6-DTBP) which has bulky side group for intra-twisted structure and blue emission. In solution state, 1,6-DTBP exhibited absorption maximum value of 365 nm and photoluminescence (PL) maximum value of 425 nm. In film state, 1,6-DTBP exhibited absorption maximum value of 373 nm and PL maximum value of 461 nm without excimer band. 1,6-DTBP can be applicable to OLED emitter as a blue emission.</P>

Blending polybenzimidazole with an anion exchange polymer increases the efficiency of vanadium redox flow batteries

Jung, Mina,Lee, Wonmi,Noh, Chanho,Konovalova, Anastasiia,Yi, Gyu Seong,Kim, Sangwon,Kwon, Yongchai,Henkensmeier, Dirk Elsevier 2019 Journal of membrane science Vol.580 No.-

<P><B>Abstract</B></P> <P>PBI membranes are recently discussed as stable, well performing membranes for vanadium redox flow batteries (VRFB). Blending meta-PBI with an anion exchange polymer (FAA3i) slightly reduces the coulomb efficiency from 99.7 to 97.8%, but strongly increases the voltage efficiency from 82.5 to 88.2%, leading to an increased energy efficiency (86.2% at 80 mA cm<SUP>−2</SUP>), exceeding that of meta-PBI (82.2%) and N212 (83%). Apparently, since the conductivity of sulfuric acid has a maximum around a concentration of 3.8 M, the concentration of the absorbed acid has a dominant influence on the conductivity. Addition of FAA3i decreases the concentration of the acid absorbed by PBI membranes. Furthermore, an ex-situ stability test in 1.5 M V<SUP>5+</SUP> solutions in 2 M sulfuric acid for 87 days showed a very high stability for meta-PBI and Nafion 212, while the commercial FAA3 membrane disintegrated into pieces. Blending of meta-PBI and FAA3 decreased the stability, as proven by formation of V<SUP>4+</SUP>, but all tested blend membranes retained their membrane shape and could still be handled. Blending with FAA3 reduces the tensile strength and Young's modulus of meta-PBI, and doping with sulfuric acid leads to a further decrease in the mechanical strength. However, an acid doped PF-21 still showed a tensile strength of 37 MPa and a Young's modulus of 0.7 GPa.</P> <P><B>Highlights</B></P> <P> <UL> <LI> PBI and FAA3 (an AEM) were blended and doped with sulfuric acid for use in VRFB. </LI> <LI> Coulomb efficiency slightly decreased, but voltage efficiency strongly increased. </LI> <LI> Energy efficiency at 80 mA/cm<SUP>2</SUP> reached 86.2%, higher than that of Nafion 212 (83%). </LI> <LI> Stability of blends against VO<SUB>2</SUB> <SUP>+</SUP> increases with amount of PBI in the blends. </LI> <LI> Doping decreases the tensile strength, but acid doped PF-21 still had a TS of 37 MPa. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Investigation on the electronic state of In-doped ZnO nanocrystals by hard X-ray photoemission spectroscopy

Mina Jung,Sunyeo Ha,Seungjun Oh,구지은,Keisuke Kobayashi,Tae-In Jeon,Yoshihiro Murakami,Jiho Chang,Takafumi Yao 한국물리학회 2009 Current Applied Physics Vol.9 No.2

ZnO:In nanocrystals (NCs) with various In contents were synthesized by using a mixed source vapor transportation method. The morphological variation and electronic structure of ZnO:In NCs were studied by bulk sensitive hard X-ray photoemission spectroscopy (HX-PES). ZnO:In NCs are classified into ZnOlike hexagonal and In2O3-like cubic groups, based on the crystal structure, and we have estimated the In content for the phase transformation to be as high as 35 atomic% (atm.%). A filled electronic state in the conduction band was observed from the ZnO-like group, which is regarded as a metallic state, due to an increase of extrinsic carrier density. ZnO:In nanocrystals (NCs) with various In contents were synthesized by using a mixed source vapor transportation method. The morphological variation and electronic structure of ZnO:In NCs were studied by bulk sensitive hard X-ray photoemission spectroscopy (HX-PES). ZnO:In NCs are classified into ZnOlike hexagonal and In2O3-like cubic groups, based on the crystal structure, and we have estimated the In content for the phase transformation to be as high as 35 atomic% (atm.%). A filled electronic state in the conduction band was observed from the ZnO-like group, which is regarded as a metallic state, due to an increase of extrinsic carrier density.

Exciplex hosts for blue phosphorescent organic light-emitting diodes

Mina Jung,Jun Yeob Lee 한국정보디스플레이학회 2020 Journal of information display Vol.21 No.1

The host material of organic light-emitting diodes (OLEDs) has been advanced from a single host to a mixed host for high efficiency and long lifetime. Several types of mixed host have been reported in the literature, but the exciplex host has been popular as the mixed host of OLEDs. The exciplex host has been developed mostly for red and green phosphorescent OLEDs, and has upgraded device performances, but it is difficult to develop the exciplex host for blue phosphorescent OLEDs. Recently, several works demonstrated the potential of the exciplex host for blue phosphorescent OLEDs. In this paper, the exciplex host for blue OLEDs is reviewed, and its prospects are presented.

The effect of frontier orbital distribution of the core structure on the photophysics and device performances of thermally activated delayed fluorescence emitters

Jung, Mina,Lee, Kyung Hyung,Hong, Wan Pyo,Lee, Jun Yeob The Royal Society of Chemistry 2019 Journal of Materials Chemistry C Vol.7 No.25

<P>The effect of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) distribution of the core structure on the thermally activated delayed fluorescence (TADF) behavior of the TADF emitters was investigated. Dibenzofuran was used as the core structure of the TADF materials, and its 2 and 3 positions were substituted with a donor and an acceptor. Two TADF emitters with the donor and acceptor positions exchanged with each other were synthesized and suggested that the substitution of the donor at the LUMO dominant position and the acceptor at the HOMO dominant position is beneficial to improve the efficiency of the TADF OLEDs. It was described that the substitution positions of the donor and acceptor to the core structure should be managed to increase the quantum efficiency of the TADF devices by enlarged orbital overlap.</P>

Highly efficient pyrene blue emitters for OLEDs based on substitution position effect

Jung, Mina,Lee, Jaehyun,Jung, Hyocheol,Kang, Seokwoo,Wakamiya, Atsushi,Park, Jongwook Elsevier 2018 Dyes and pigments Vol.158 No.-

<P><B>Abstract</B></P> <P>To investigate the effect of substitution position of the side group on a pyrene core, three derivatives having a triphenylbenzene group as a bulky side group at the 1,6-position, 4,9-position, and 1,8-position were successfully synthesized: 1,6-bis(5′-phenyl-[1,1':3′,1″-terphenyl]-4-yl)pyrene (1,6-DTBP), 4,9-bis(5′-phenyl-[1,1':3′,1″-terphenyl]-4-yl)pyrene (4,9-DTBP), and 1,8-bis(5′-phenyl-[1,1':3′,1″-terphenyl]-4-yl)pyrene (1,8-DTBP). The three synthesized materials showed excellent thermal stability with a high T<SUB>g</SUB> of >140 °C and a high T<SUB>d</SUB> of >500 °C. Due to the highly twisted structure of 1,8-DTBP in the film state, the absolute photoluminescence quantum yield value was improved. Of the three synthesized materials used as an emitter in a non-doped organic light-emitting diode device, 1,8-DTBP showed highly efficient electroluminescence performance, with a luminance efficiency of 6.89 cd/A, power efficiency of 3.03 lm/W, and external quantum efficiency of 7.10% at 10 mA/cm<SUP>2</SUP>. In addition, 4,9-DTBP showed a deep-blue emission of CIE x, y (0.158, 0.063) suitable for HD-TV.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 1,8-DTBP showed highly efficient electroluminescence performance of external quantum efficiency of 7.10%. </LI> <LI> The EQE value of 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP was 1.59%, 3.47%, and 7.10%. </LI> <LI> 4,9-DTBP had a deep-blue emission of CIE x, y (0.158, 0.063), satisfying the HD-TV requirements due to its wide band gap. </LI> </UL> </P>

Porous-Nafion/PBI composite membranes and Nafion/PBI blend membranes for vanadium redox flow batteries

Jung, Mina,Lee, Wonmi,Nambi Krishnan, N.,Kim, Sangwon,Gupta, Gaurav,Komsiyska, Lidiya,Harms, Corinna,Kwon, Yongchai,Henkensmeier, Dirk Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.450 No.-

<P><B>Abstract</B></P> <P>Although Nafion membranes have a high chemical stability against VO<SUB>2</SUB> <SUP>+</SUP> and a low resistance, their low coulomb efficiency (CE), due to crossover of vanadium cations, should be addressed. PBI membranes are chemically stable and effectively block vanadium cations, but have a lower conductivity than Nafion. Here we describe the fabrication of layered membranes, which consist of a 40 µm thick porous Nafion layer and a 2–17 µm thin PBI blocking layer. To promote adhesion, a <2 µm thick layer of a 1:1 Nafion/PBI blend is introduced between the outer layers. While this bonding layer is necessary to promote adhesion, the strong ionic interactions between Nafion and PBI reduce the acid uptake. Immersed in 1 M sulfuric acid (SA), the weight of meta-PBI increases 17%, while that of NP1:3, NP1:1 and NP3:1 only increases 16%, 8% and 7%, respectively. This decreases the conductivity in 2 M SA from 2.8 mS cm<SUP>−1</SUP> for meta-PBI to 1.5, 0.4 and 0.04 mS cm<SUP>−1</SUP> for NP1:3, NP1:1 and NP3:1, respectively. The initial CE of a flow battery using p-Nafion-1:1-PBI20 was as good as one with Nafion 212 (93% at 80 mA cm<SUP>−2</SUP>), while one with p-Nafion-1:3-PBI3 showed exactly the same voltage efficiency as one with Nafion 212.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A trilayer membrane of porous Nafion, an adhesion promoting layer and PBI. </LI> <LI> The layers are applied on porous Nafion by spray coating. </LI> <LI> Polybenzimidazole (PBI) reduces crossover of vanadium ions in flow batteries. </LI> <LI> A blend of Nafion and PBI promotes adhesion but increases ionic resistance. </LI> <LI> The closed pores in Nafion are not easily filled with acid and increase resistance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Realization of a Low-Threshold-Voltage Field Emitter by Using High-Quality ZnO Nano-Tetrapods

Mina Jung,Dongchul Oh,고항주,Hyunchul Ko,Jiho Chang,Sunyeo Ha,Takafumi Yao,Wookhyun Lee 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6

High-performance ZnO tetrapods-type field emitters with low turn-on voltage are realized. Systematic investigations of the formation conditions are performed. Tetrapod-shaped ZnO nanostructures are formed on Si substrates by using a vapor phase transportation method. The effects of two important growth parameters, the growth temperature and the VI/II ratio, are investigated. The growth temperature is controlled in the range from 600 C to 900 C while the VI/II ratio is adjusted by changing the flux of the carrier gas. ZnO tetrapods, formed at 800 C under a carrier gas flux of 0.5 cc/mm2min, show a uniform shape with 100-nm-thick and 1 1.5-μm- long legs. Also, the growth condition confirms a stoichiometric chemical composition (O/Zn 1) without any second phases. The excellent luminescence properties, a strong excitonic UV emission at 3.25 eV without deep-level emission, indicate that tetrapod structures with high crystallinity can be formed under optimized growth conditions.쵇

직류 수용가를 위한 전류원 다채널 컨버터의 스위칭 알고리즘

김민아(Mina Kim),정지훈(Jee-Hoon Jung),오승열(Seung-Yeol Oh),최정식(Jung-Sik Choi),차대석(Dea-Seak Cha),고병선(Byoung-Sun Ko) 대한전기학회 2023 대한전기학회 학술대회 논문집 Vol.2023 No.4-1