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Hwang, Jaeyoung,Ji, Seung-Bae,Cheon, Hyungjin,Yook, Kyoung Soo,Kwon, Soon-Ki,Kim, Yun-Hi Elsevier 2018 Dyes and pigments Vol.149 No.-
<P><B>Abstract</B></P> <P>Two heteroleptic iridium complexes, (dmppy)<SUB>2</SUB>Ir(tmd) and (dmppy)<SUB>2</SUB>Ir(acac), which consist of phenylpyridin (ppy) as main ligand with dimethyl substituents on both the phenyl ring and the pyridine ring, and heptanedione (tmd) and acetyl acetonate (acac) as ancillary ligands were synthesized and characterized regarding their suitability as orange organic light-emitting diodes (OLEDs). The photoluminescence (PL) of (dmppy)<SUB>2</SUB>Ir(tmd) and (dmppy)<SUB>2</SUB>Ir(acac) produced orange emissions with maximum emission peaks at 577 and 570 nm, respectively. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital energy (LUMO) levels of (dmppy)<SUB>2</SUB>Ir(tmd) and (dmppy)<SUB>2</SUB>Ir(acac) were −5.03/-2.83 and −5.02/-2.77 eV, respectively. An optimized non-halogenated solution-processed (dmppy)<SUB>2</SUB>Ir(tmd) device showed a high current efficiency of 52.7 cd/A and exhibits an efficiency of 89% when compared to a vacuum-deposited device that showed 66.7 cd/A at 1000 cd/m<SUP>2</SUP>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Two heteroleptic iridium complexes were designed for orange emitters. </LI> <LI> We fabricated the non-halogenated solution-processed PHOLEDs. </LI> <LI> Maximum current efficiencies of 57.5 cd/A ((dmppy)<SUB>2</SUB>Ir(tmd)) and 43.5 cd/A ((dmppy)<SUB>2</SUB>Ir(acac)) were achieved. </LI> </UL> </P>
Hwang Jaeyoung,Jin Joon-Hyung,장미경,Lee Kang Yeol,Yang In-Hwan 한국물리학회 2022 Current Applied Physics Vol.35 No.-
Carbon coated MnOx-Ni foam electrodes were successfully prepared using a combined process of hydrogel reaction followed by high-temperature pyrolysis under air or Ar gas conditions. The prepared samples were analyzed by various characterization tools. To evaluate the performances of the carbon coated MnOx-Ni foam electrodes as supercapacitors, cyclic voltammetry (CV), galvanostatic charge–discharge, electrochemical impedance spectroscopy (EIS) and cycle stability were also carried out. The carbon coated MnOx-Ni foam electrodes displayed supercapacitive behavior in 1.0 M KOH with a high specific capacitance value of 354.6 F g− 1 at 10 mV s − 1 . The electrode also exhibited remarkable cycle stability. This research provides a valuable and effective approach to enhance the performance of materials applied as supercapacitors.
Hwang, Jaeyoung,Park, Jeonghun,Kim, Yu Jin,Ha, Yeon Hee,Park, Chan Eon,Chung, Dae Sung,Kwon, Soon-Ki,Kim, Yun-Hi American Chemical Society 2017 Chemistry of materials Vol.29 No.5
<P>The organic solar cell (OSC) performance of a series of new donor acceptor copolymers containing indolo[3,2b]indole as a key donor block and benzothiadiazole (BT) units with various degrees of fluorination as acceptors is reported. Compared with the simple carbazole unit, the strategically developed indolo[3,2-b]indole unit is found to significantly extend pi-conjugation and thus increase the intermolecular interactions of the resulting copolymer, as probed by density functional theory calculations, photophysical studies, and structural/morphological analyses. In addition, fluorination of BT can facilitate nano structuring of the copolymers, mainly due to further planarization of the backbone, which leads to apparently higher hole/electron charge carrier mobilities. The OSC properties of this series of new copolymers blended with fullerene show a strong dependence on the fine and continuous fibrous nanostructure of the blend film. The indolo[3,2-b]indole-based copolymer with singly fluorinated BT units possesses optimal intermolecular interactions and achieves the highest power conversion efficiency of 8.84% under AM 1.5G illumination. This result shows the potential of z-extended carbazole moieties for achieving high-performance OSCs with many of the favorable properties induced by large heteroacene blocks.</P>
Enhancement of nanofluid stability and critical heat flux in pool boiling with nanocellulose
Hwang, Won-Ki,Choy, Seunghwan,Song, Sub Lee,Lee, Jaeyoung,Hwang, Dong Soo,Lee, Kwon-Yeong Applied Science Publishers 2019 Carbohydrate polymers Vol.213 No.-
<P><B>Abstract</B></P> <P>A nanofluid, which is an aqueous fluid with nanoparticles, is an attractive medium for enhancing critical heat flux (CHF); however, its instability over a long period of time due to sedimentation and aggregation has impeded its successful application in industry. In this study, lightweight negatively charged TEMPO-oxidized cellulose nanofibers (CNFs) were utilized as a nano-sized substance in water and examined to enhance both the CHF performance and thermal stability of nanofluids. Owing to low density of the CNFs and long range repulsion between negatively charged CNFs, there were no aggregation and sedimentation of CNFs with multiple boiling/cooling cycles. In addition, with CNF concentrations of 0.01, 0.03, 0.05, and 0.10 wt%, CHF enhancement increases of 40.7%, 45.1%, 54.9%, and 69.4%, respectively, were achieved over that of pure water. The present results demonstrated the great potential of CNFs as eco-friendly and cost-effective nano-substances that can overcome the instability of nanofluids.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nanofluid containing cellulose nanofibers (CNFs) enhanced critical heat flux (CHF). </LI> <LI> Chemical inertness and self-repulsiveness of CNFs manifested stable pool boiling. </LI> <LI> Nanofibrous structure was beneficial for CHF enhancement. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Alternative nanofluid containing carboxylated nanocellulose exhibits enhanced critical heat flux (CHF) and stable dispersion during pool boiling.</P> <P>[DISPLAY OMISSION]</P>