Ho-Yeol Park

Highly efficient deep-red emitting methyl substituted thiophenylquinoline based Ir(III) complexes for solution-processed organic light-emitting diodes

ABSTRACT Herein, we synthesized two new methyl substituted thiophenyl-quinoline based heteroleptic Ir(III) complexes as guest molecules for deep-red emitting solution-processed phosphorescent organic light-emitting diodes (PhOLEDs). Their thermal stabilities, photophysical properties and electroluminescence (EL) properties are systematically investigated. (MTPQ)2Ir(pic) and (MTPQ)2Ir(acac) showed photoluminescence emission of 614 and 629 nm and a photoluminescence quantum yield of 21% and 15%, respectively. Solution-processed deep-red emitting PhOLEDs were fabricated using standard structure with PEDOT:PSS and TPBi as hole and electron transport layers, respectively and, a mixed host of TCTA:TPBi (1:1) doped with the guest Ir(III) molecules. The emission electroluminescence wavelength was slightly red shifted by 11 nm for both (MTPQ)2Ir(pic) (625 nm) and (MTPQ)2Ir(acac) (640 nm). A maximum external quantum efficiency of 8.46% and maximum current efficiency of 7.37 cd/A was achieved for (MTPQ)2Ir(pic) with a deep-red CIE coordinates of (0.679, 0.318).

Poly(N-bromo-2-ethynylpyridinium bromide) for quasi-solid state dye-sensitized solar cell applications

ABSTRACT A new conjugated ionic polymer, poly(N-bromo-2-ethynylpyridinium bromide) (PBEPB) was applied for a quasi-solid-state dye-sensitized solar cells (DSSCs) and compared the device performance with poly(N-bromo-2-ethynylpyridinium iodide) (PBEPI) as reference cell. The polymer was prepared by the spontaneous polymerization of 2-ethynylpyridine using bromine. The PBEPB was completely soluble in such organic solvents as DMF, DMSO and NMP etc. The photoluminescence peaks of PBEPB was observed at 407 nm and 516 nm, which corresponds to the photon energy of 3.15 eV and 2.41 eV, respectively. Quasi-solid-state DSSCs with a SnO2:F/TiO2/D719 dye/solid-state electrolyte/Pt device was fabricated with an ionic conjugated polymer with pyridinium substituents, which shows the power conversion efficiency (PCE) of 5.95%.

Impact of Topology of Alkoxy Side Chain in Alkoxyphenylthiophene Subsituted Benzodithiophene Based 2D Conjugated Low Bandgap Polymers on Photophysical and Photovoltaic Properties

We report a new series of low band gap (LBG) polymers (P1-P4), in which para or meta- alkoxyphenylthiophene (APTh) substituted benzodithiophene and 2,5-ethylhexyl-3,6-bis(5-bromothiophen-2-yl)pyrrolo[3,4-c]-pyrrole-1,4-dione or 2-ethylhexyl-4,6-dibromo-3-fluorothieno[3,4-b]thiophene-2-carboxylate are key repeating units. All the polymers showed broad absorption profiles over 900 nm with reduced optical band gaps (Egopt). Interestingly, the straightforward modification (exchanging the topology of alkoxy side chain on phenyl group of APTh in donor unit) brought considerable changes in photophysical and photovoltaic properties of new polymers. In particular, meta-substituted polymers (P2, P4) showed reduced Egopt (1.26, 1.41 eV), deep highest occupied molecular orbitals (HOMOs) (-5.23, -5.28 eV) than para-substituted polymers P1, P3 (Egopt=1.33, 1.44 eV; HOMOs=-5.19, -5.20 eV). Furthermore, the optimized P2 and P4 based devices delivered an enhanced power conversion efficiency (PCE) of 4.39 and 4.33%, with open-circuit voltage (Voc) of 0.71 and 0.79 V, respectively, which are higher than P1 (PCE of 2.95 with Voc of 0.65) and P3 (PCE of 2.33% with Voc of 0.69 V) based devices.

High efficient vacuum deposited red organic light-emitting diodes compared with their solution-processed counterpart

ABSTRACT Herein, we demonstrate dry- and wet-process feasible red (PhQ-Th)3Ir complex as dopant and improved external quantum efficiency (EQE) of the device by 30.17% though vacuum-process using the same device structure. The turn-on voltage is reduced to less than 3 V by adopting vacuum deposition process. The vacuum-processed devices showed EQE and power efficiency of 26.75% and 28.90 lm/W, respectively, with turn on voltage of 2.83 V. The maximum luminance is increased from 1088 cd/m2 to 6396 cd/m2 using dry-process. It is found that the difference in device performance is attributed to their morphological variance of solution- and vacuum-processed devices.