Jongchul Kwon

A bipolar host containing 1,2,3-triazole for realizing highly efficient phosphorescent organic light-emitting diodes

We have developed a novel host material, 9,9′-(2-((4-phenyl-1,2,3-triazol-1-yl)methyl)biphenyl-4,4′-diyl)biscarbazole (CBP-TA), for realizing highly efficient blue phosphorescent OLEDs. The maximum external quantum efficiency of the OLED device developed using CBP-TA doped with a blue phosphorescent material was 30% greater than that of a CBP-based device. This enhanced external quantum efficiency resulted from the bipolar properties of the new host, owing to which well-balanced hole and electron transport through the emitting layer was achieved. The excellent bipolar carrier transport properties of the new host were experimentally verified using various OLED device data.

New Organic Dye Based on a 3,6-Disubstituted Carbazole Donor for Efficient Dye-Sensitized Solar Cells

We have synthesized and characterized four organic dyes (H1-H4) based on a 3,6-disubstituted carbazole donor as sensitizers in dye-sensitized solar cells. These dyes have high molar extinction coefficients and energy levels suitable for electron transfer from an electrolyte to nanocrystalline TiO(2) particles. Under standard air mass 1.5 global (AM 1.5 G) solar irradiation, a device using dye H4 exhibits a short-circuit current density (J(sc)) of 13.7 mA cm(-2), an open-circuit voltage (V(oc)) of 0.68 V, a fill factor (FF) of 0.70, and a calculated efficiency of 6.52%. This performance is comparable to that of a reference cell based on N719 (7.30%) under the same conditions. After 1000 hours of visible-light soaking at 60 °C, the overall efficiency remained at 95% of the initial value.

Signal amplification via intramolecular energy transfer using tripodal neutral iridium(III) complexes upon binding to avidin.

A neutral tripod system for biotin-avidin assays, which is composed of biotin, FIrpic as an energy acceptor, and mCP as an energy donor, offers remarkable sensitivity over traditional transition metal based protein probes due to the intramolecular energy transfer and increased hydrophobicity associated with the avidin binding site and neutral probe 1.

Effect of main ligands on organic photovoltaic performance of Ir(III) complexes

The photovoltaic performance of devices fabricated using three iridium complexes (1, 2, and 3) containing different main ligands (1-phenylisoquinoline, (4-isoquinolin-1-yl-phenyl)diphenylamine, and 1-pyren-1-yl-isoquinoline for 1, 2, and 3, respectively) was investigated. Two different devices, one fabricated by spin coating and one produced by vacuum deposition, were tested. Among the bulk heterojunction solar cells (BHJCs) fabricated by spin coating, the cell fabricated using 2 had the highest power conversion efficiency (PCE, 0.50%). The PCEs of 1 and 3 were 0.43% and 0.34%, respectively. These results suggested that the superior hole-transport ability of the triphenylamine moiety in 2 was responsible for the high photovoltaic performance of the device fabricated using this complex. This assumption was confirmed by fabricating electron-only devices using the three Ir complexes and comparing the turn-on voltage of each device. The photovoltaic performance of device C fabricated by the vacuum co-deposition of 2 and C60 in a 50 nm-thick active layer was 50% higher than that of device A (bilayer heterojunction solar cell) and device B (fabricated by the co-deposition of 2 and C60 with a 30 nm-thick active layer).

Pyrene end-capped oligothiophene derivatives for organic thin-film transistors and organic solar cells

We have demonstrated an efficient one-step synthesis of pyrene end-capped thiophene oligomers as active materials for organic thin-film transistors (OTFTs) and donor materials for organic solar cells (OSCs). In particular, the OTFT device based on 5,5′′-di(pyren-1-yl)-2,2′:5′,2′′-terthiophene (3s) exhibited a reasonable field effect mobility of 0.11 cm2 V−1 s−1, and a power conversion efficiency of 1.20% was achieved when 3s was used as active materials in OSCs. These pyrene end-capped thiophene oligomers are considered to be good organic semiconducting materials for OTFTs and OSCs.

Solution processable donor materials based on thiophene and triphenylamine for bulk heterojunction solar cells

Solution processable and thermally stable donor materials 2,5-bis[4-(N,N-diphenylamino)styryl] thiophene (1) and 2,5-bis[4-(N,N-diphenylamino)styryl]-2,2′-bithiophene (2) were synthesized for bulk heterojunction solar cells, which consist of a thiophene, or bithiophene and triphenylamine unit linked with conjugated bonds. The best device performance, optimized at 1:PCBM = 1:3 and 2:PCBM = 1:4, exhibited the maximum open circuit voltages of 0.56 and 0.51 V, short circuit currents of 1.33 and 1.88 mA cm−2, and power conversion efficiencies of 0.23 and 0.34%, respectively, under simulated AM 1.5 solar irradiation at 100 mW cm−2.

Efficient blue phosphorescent host through nonbonded conformational locking interactions

We developed a new host material TCTEB with a conformationally homogeneous, sterically bulky structure due to nonbonded interactions between adjacent methylene groups. The host presented good thermal stability (Tg = 122 °C and Td = 321 °C) and high triplet energy (3.0 eV). The maximum quantum efficiency, current efficiency and power efficiency of the OLED device using the TCTEB host were 8.5%, 13.7 cd A−1, and 11.3 lm W−1, respectively, when doped with 8 wt% FIrpic.

Improvement of TERCOM aided inertial navigation system by velocity correction

TERCOM is a terrain referenced navigation system using batch processing method which determines vehicles current position by comparing a series of terrain height measurements with database. Generally, it is known that TERCOM operates well over terrain with high roughness. However, if the attitude and velocity error of INS is not corrected, the navigation solution of conventional TERCOM aided INS can diverge. This paper describes the TERCOM aided INS algorithm and show the divergence problem. To solve the problem, we propose an improved TERCOM aided INS algorithm which corrects the velocity error of INS using linear Kalman filter, even though the navigation system does not have a speedometer. It is shown that the proposed TERCOM algorithm can prevent divergence of navigation solution based on computer simulations.

Vacuum processable donor material based on dithieno[3,2-b:2′,3′-d]thiophene and pyrene for efficient organic solar cells

We have developed a new donor material, 2,6-di(pyren-1-yl) dithieno[3,2-b:2′,3′-d]thiophene (DDT), consisting of dithieno[3,2-b:2′,3′-d]thiophene (DTT) and pyrene units. The bulk heterojunction (BHJ) device based on DDT : C70 = 1 : 4 exhibited an efficient power conversion efficiency (PCE) of 3.60%, under simulated AM 1.5 solar irradiation at 100 mW cm−2.