Se-Young Oh

Synthesis and Hole-Transporting Properties of Phenyl-Carbazyl Derivatives

We synthesized new hole-transporting material, 9,9′-diphenyl-9H,9′H-3,3′-bicarbazole(P-Cvz-2), 9,9′-diphenyl-6-(9-phenyl-9H-carbazol-3-yl)-9H,9′H-3,3′-bicarbazole(P-Cvz-3), 6-(9,9′-diphenyl-9H,9′H-3,3′-bicarbazol-6-yl)-9,9′-diphenyl-9H,9′H-3,3′-bicarbazole(P-Cvz-4A) and 9-phenyl-6-(9-phenyl-9H-3,9′-bicarbazol-6-yl)-9H-3,9′-bicarbazole(P-Cvz-4B). EL luminance efficiencies of P-Cvz-2, P-Cvz-3, P-Cvz-4A and P-Cvz-4B devices were found to be 5.24, 5.64, 4.86 and 4.94 cd/A at 50 mA/cm2, respectively, when synthesized materials are using as a HTL material. The luminance efficiency of P-Cvz-3 is 20% higher than that of NPB, a commercialized HTL material used as a reference in this study.

Electrochemical immunosensor for prostate-specific antigen using self-assembled oligophenylethynylenethiol monolayer containing dendrimer.

Electrochemical immunosensor for prostate-specific antigen (PSA) was fabricated with a self-assembled 4-(2-(4-(acetylthio)phenyl)ethynyl)benzoic acid (APBA) as a bioreceptor. In order to enhance the electrochemical activity of PSA detection, poly(amidoamine) dendrimer was linked on the APBA self-assembled monolayer (SAM). The formation and electrical properties of the SAMs were investigated by surface plasmon resonance and cyclic voltammetry, respectively. The surface morphology of PSA sandwich complex onto the APBA SAM was studied by atomic force microscopy.

Synthesis and Properties of Poly(10-Octylphenothiazine-CO-2′,3′,6′,7′-Tertrakis-Octyloxy-9-Spirobifluorene) for OLEDs

Many attempts have been focused on polymer light-emitting diodes (PLEDs) for large area display application. We report synthesis and properties of new phenothiazyl polymer derivatives, Poly(10-octyl-10H-phenothiazine-3,7-diyl) (POP), Poly(2′,3′,6′,7′-tertrakis-octyloxy-9-spirobifluorene-2,7-diyl) (PTOSF), and their random copolymers, Poly(10-octylphenothiazine-co-2′,3′,6′,7′-tertrakis-octyloxy-9-spirobifluorene) (POTOSF), which were polymerized by Yamamoto reaction. The obtained compound was identified by 1H-NMR, UV-Visible spectroscopy and GPC data. Weight average molecular number (Mn) of the polymers ranged from 17,000 to 300,000 g/mol with polydispersity indices of 1.6 ∼ 6.5. Maximum UV-Visible absorption of the polymers was distributed from 285 to 403 nm. PL emission of POP, PTOSF and POTOSF copolymer were found to be 480, 434 and 484 nm, respectively. EL emission peak of double-layer EL device of POTOSF was at 494 nm (bluish green).

Improving the performance of organic solar cells using an electron transport layer of B4PyMPM self-assembled nanostructures

The electron transport (ETL) layer improves power conversion efficiency (PCE) in organic photovoltaic cells (OPVs) through the incorporation of the cathode interfacial layers. Here, we introduce [bis-4,6-(3,5-di-4-pyridylphenyl)-2-methylpyrimidine] (B4PyMPM) as an n-type buffer layer consisting of a self-organized layer with a horizontal configuration in bulk heterojunction OPVs. It is demonstrated that self-organization of this B4PyMPM compound in which molecules adopt a horizontal orientation parallel to the organic semiconducting substrate induces a large local interfacial electric field that results in a significant enhancement of exciton dissociation. The device using B4PyMPM as an ETL layers has a significantly high open circuit voltage (Voc = 0.64 V), good short circuit current (Jsc = 8.24 mA/cm2), good fill factor (FF = 0.65) and good PCE (3.42%). The physical properties of the device have also been studied from the measurements of impedance spectroscopy and photocurrent, which directly show the mechanisms occurring inside OPVs.

Fabrication of self-assembled oligophenylethynylenethiol monolayer for electrochemical glucose biosensor

An electrochemical glucose biosensor was developed using a gold (Au) electrode, which was composed of self-assembled oligophenylethynylenethiol monolayer and glucose oxidase (GOx) structure. Oligophenylethynylenethiol was used as a chemical linker for the immobilization of GOx on Au electrode, which facilitates the transfer of electron produced by enzyme reaction to the Au electrode. The electrical property of self-assembled oligophenylethynylenethiol monolayer was investigated by using cyclic voltammetry (CV). The formation of self-assembled oligophenylethynylenethiol monolayer and GOx layer on Au surface was verified by using atomic force microscopy (AFM) and surface plasmon resonance (SPR). The electrochemical glucose biosensor exhibited a linear relationship between target concentration and oxidation current in the range of 2-30mM and its detection limit was 2mM.

Anthracene Effects on Organic Light Emitting Diode Performance of Tetra-Substituted Ethylene Derivatives

We synthesized new bluish-green and sky-blue emitting materials, 1,1,2,2-tetrakis(4′-tert-butylbiphenyl)ethane[TBBPE] and 1,1,2,2-tetrakis(4-(anthracen-9-yl)phenyl)ethene[TAPE]. TBBPE and TAPE film showed PL maximum value of 511 nm and 492 nm. TBBPE OLED device showed bluish-green C.I.E. value of (0.236, 0.412) and high luminance efficiency of 5.02 cd/A at 10 mA/cm2. TAPE device also showed sky-blue C.I.E. value of (0.213, 0.323) and 3.17 cd/A at 10 mA/cm2. It is found that TBBPE shows better luminance efficiency than TAPE and TAPE device exhibits relatively lower operating voltage and better C.I.E. value than TBBPE device.

Crystalline nanostructure and morphology of TriF-IF-dione for high-performance stable n-type field-effect transistors

The device performance and stability of n-type organic field-effect transistors (OFETs) based on 1,2,3,7,8,9-hexafluoro-indeno[1,2-b]fluorene-6,12-dione (TriF-IF-dione) were investigated. The electrical characteristics of TriF-IF-dione FETs were optimized by systematically controlling the dielectric surface properties via insertion of organic interlayers, such as self-assembled monolayers (NH2–, CH3–, and CF3–) or polymeric layers (polystyrene, PS) at the semiconductor–SiO2 dielectric interfaces. In particular, a thin PS buffer layer on the SiO2 surface provided a device that performed well, with a field-effect mobility of 0.18 cm2 V−1 s−1 and an on–off current ratio of 4.4 × 106. The improvements in the performance of TriF-IF-dione OFET conveyed by the PS interlayers were examined in terms of the crystalline nanostructure and the charge modulation effects in the channel. These properties were strongly correlated with, respectively, the hydrophobicity and the electron-donating characteristics of the dielectric surface. The TriF-IF-dione FETs with a PS interlayer showed excellent electrical stability attributed to high activation energies for charge trap creation. A complementary inverter comprising both p-type pentacene and n-type TriF-IF-dione was also successfully demonstrated.

Optimal-Fabrication Conditions of Cytochrome c LB Films

Abstract The optimal fabrication condition of cytochrome c Langmuir-Blodgett (LB) film was investigated. To verify the pH dependence of cytochrome c film formation, the various π-A isotherms were obtained at pH 6.0, 7.0, 8.0, 9.0, and 10.0, respectively. The cytochrome c LB films were then fabricated onto the quartz substrate, and the deposition of cytochrome c LB films was investigated by UV-visible spectroscopy.

New Multi-Phenylated Carbazole Derivatives for OLED through Diels-Alder Reaction

We synthesized multi-phenylated carbazole derivatives such as 3,6-Bis[(2,3,4,5-tetraphenyl)phenyl]-9-ethylcarbazole(BTPEC) and 3,6-Bis(7,10-diphenyl-fluoranthene)-9-ethlycarbazole(BDPEC), through Diels-Alder reaction. These products were identified by NMR, Fab-Mass analysis. Electro-optical properties of these materials were characterized by cyclic voltammetry (CV) and, UV-visible and photoluminescence (PL) spectra. The maximum absorbance of BTPEC appeared at 307 nm and BDPEC showed maximum absorbance of 307 nm and 388 nm. And two compounds also exhibited PL peaks at 389 nm and 483 nm. When we used these two materials as hole injection layer(HIL) and hole transport layer(HTL) in OLED device, the devices showed about 3 cd/A and 2 cd/A, respectively.

Studies on the fabrication and characteristics of organic photodiode using novel Ga-doped NiOx as an electron-blocking layer

ABSTRACT The photodiode converts incident light into a microcurrent that flows when photons of sufficient energy strike the device under reverse bias. In doing so, a leakage current is caused by the reverse bias. In order to decrease the leakage current, buffer layers are introduced as electron- and hole-blocking materials between the photoactive material and electrode. We fabricated an organic photodiode using Ga-doped NiOx as an electron-blocking layer and investigated the physical effects of Ga doping on the performance of the organic photodiode. Our results showed that this diode exhibited high detectivity of 1.06 × 1012 Jones.