Suchergebnisse

Polymer-based blue electrophosphorescent light-emitting diodes are reported by doping bisorthometalated (phosphine)cyanoiridium(III) complex Ir(ppy)2P(n-Bu)3CN (ppy = 2-phenylpyridine, P(n-Bu)3 = tri-n-butylphosphine) in poly(vinylcarbazole) (PVK) as the source of emission. The (phosphine)cyanoiridium(III) complex shows sky blue emission with two peaks at 467 and 496 nm originating from an admixture of triplet metal-to-ligand charge-transfer and ligand-centered states. The PL and EL spectra of an Ir(ppy)2P(n-Bu)3CN-doped PVK film and device exhibited no emission from PVK, indicating that the energy transfer from PVK to Ir(ppy)2P(n-Bu)3CN is efficient. A maximum external quantum efficiency (ηex) of 1.45% and power efficiency (ηp) of 0.99 lm/W were achieved at 13 and 6 mA/cm2 at a 10 wt % doping concentration, respectively. ; This work was financially supported by CRM-KOSEF, Korea University, and Dongwoo Fine-Chem Co., Ltd. R.R.D. is thankful to the government of Orissa, India, for granting a study leave.

Air stable n-type organic field effect transistors (OFETs) based on C60 are realized using a perfluoropolymer as the gate dielectric layer. The devices showed the field-effect mobility of 0.049 cm2/V s in ambient air. Replacing the gate dielectric material by SiO2 resulted in no transistor action in ambient air. Perfluorinated gate dielectric layer reduces interface traps significantly for the n-type semiconductor even in air. ; This research was supported by a Grant (F0004071-2007-23) from the Information Display R&D Center, one of the 21st Century Frontier R&D Program funded by the Ministry of Commerce, Industry and Energy of the Korean Government.

Thickness dependence of photoluminescence (PL) efficiency and spectral shape of phosphorescent organic thin films is investigated and theoretically analyzed. The PL efficiency increases with increasing thickness to reach the maximum 92% at around 50 nm. It reduces to 77% at the thickness of 130–140 nm and oscillates between the values upon further increment of thickness. The quenching of excitons at the surface of organic layer significantly reduces the PL efficiency when the film is very thin. If the film is thicker than the critical thickness for the waveguiding of emitted light, the waveguided power is absorbed during the propagation through the organic layer so that apparent PL efficiency is reduced by the amount. Microcavity effect formed by quartz/organic layer/air also affects the PL efficiency. The appropriate thickness to obtain the PL efficiency close to the intrinsic value of a film is just the critical thickness for waveguiding through the film. ; This work was supported by a grant from the MKE of Korea Government through the center for OLED.

We report substrate thermal conductivity effect on heat dissipation and lifetime improvement of organic light-emitting diodes (OLEDs). Heat dissipation behavior of top-emission OLEDs fabricated on silicon, glass, and planarized stainless steel substrates was measured by using an infrared camera. Peak temperature measured from the backside of each substrate was saturated to be 21.4, 64.5, and 40.5 °C, 180 s after the OLED was operated at luminance of 10 000 cd/m2 and 80% luminance lifetime was about 198, 31, and 96 h, respectively. Efficient heat dissipation through the highly thermally conductive substrates reduced temperature increase, resulting in much improved OLED lifetime. ; This work supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD, Basic Research Promotion Fund) (Grant No. KRF-2008-331-D00216).

A series of new 9-phenylcarbazole (Cz-Ph)-based host materials with 1,2,4-trizole (TAZ) were synthesized for blue-emitting electrophosphorescent device. The substitution position of Cz-Ph on TAZ ring did not influence photoluminescence maximum (band gap) but the triplet energy level (T1). The electron mobility of 3,5-bis-(3-(9-carbazoyl)-phenyl)-4-(4-butyl-phenyl)-4H-[1,2,4]triazole (6) is 10 times higher than the hole mobility. This is due to the electron transporting/hole blocking characteristics of TAZ moiety. The triplet energy level of the new host materials ranges from 2.8 to 3.0 eV which are suitable for blue-emitting electrophosphorescent devices. The time-resolved photoluminescence decay curve of 4% of FIrpic (iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate) doped in the film of compound 6 showed a single exponential decay curve with a lifetime of 1.2 μs. The absolute PL quantum efficiency (ηPL) of 6 doped with 4% of FIrpic was (82 ± 2%), which is significantly higher than the case of commonly used CBP (4,4′-bis-(9-carbazoyl)-biphenyl) (44 ± 2%). These results also strongly support that triplet excitons formed in FIrpic was not transferred to 6. For a device based on 6 (ITO/PEDOT:PSS (40 nm)/NPB (15 nm)/6:6% FIrpic (30 nm)/BAlq (35 nm)/LiF (1 nm)/Al (100 nm), the maximum photometric efficiency was 14.2 cd/A at a current density of 1.1 mA/cm2, which is higher than that observed with a device based on CBP (ITO/PEDOT:PSS (40 nm)/NPB (30 nm)/CBP:6% FIrpic (40 nm)/BAlq (30 nm)/LiF (1 nm)/Al (100 nm)). ; This work was supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD, Basic Research Promotion Fund) (KRF-2006-D00552). Do.Y. Yoon acknowledges Molecular Engineering Program of the Brain Korea 21 program.

The thin-film passivation of organic light-emitting diodes (OLEDs) by a SiNx film grown by catalyzer-enhanced chemical vapor deposition was investigated. Using a tungsten catalyzer connected in series, a high-density SiNx passivation layer was deposited on OLEDs and bare polycarbonate (PC) substrates at a substrate temperature of 50 °C. Despite the low substrate temperature, the single SiNx passivation layer, grown on the PC substrate, exhibited a low water vapor transmission rate of (2–6)×10−2 g/m2/day and a high transmittance of 87%. In addition, current-voltage-luminescence results of an OLED passivated with a 150-nm-thick SiNx film compared to nonpassivated sample were identical indicating that the performance of an OLED is not critically affected by radiation from tungsten catalyzer during the SiNx deposition. Moreover, the lifetime to half initial luminance of an OLED passivated with the single 150-nm-thick SiNx layer was 2.5 times longer than that of a nonpassivated sample. ; This work was supported by Korea Research Foundation Grant funded by Korea Government (MOEHRD: Basic Research Promotion Fund)(KRF-2006-331-D00243) and Ministry of Commerce, Industry and Energy. Experiments at PLS were supported in part by MOST and POSTECH.

Two novel organic semiconductors based on arylvinylanthracene have exhibited good electrical performance (up to 0.2 cm2 V-1 s-1) on OTS treated SiO2/Si at a low substrate deposition temperature and can be easily synthesized in large quantities. ; This work was supported by grants (F0004030-2007-23, F0004071-2007-23) from the Information Display R&D Center, one of the 21st Century Frontier R&D Program funded by the Ministry of Commerce, Industry, and Energy of the Korean Government, and Seoul R&BD.

We have synthesized two novel organic semiconductors, which have a symmetrically substituted thienylvinylene anthracene backbone. They show good electrical performances on SiO2/Si, with high field-effect mobilities of up to 0.4 cm2 V-1 s-1, and can easily be synthesized in large quantities. In addition, the high mobility of such semiconductors can be achieved at low substrate deposition temperatures. ; This work was supported by grants (F0004030-2007-23, F0004071-2007-23) from the Information Display R&D Center, one of the 21st Century Frontier R&D Programs funded by the Ministry of Commerce, Industry, and Energy of the Korean Government, and Seoul R&BD.

Transparent and low resistance amorphous ZnO-doped In2O3 (IZO) anode films were grown by radio-frequency (rf) sputtering on an organic passivated polyethersulfone (PES) substrate for use in flexible organic light-emitting diodes (OLEDs). Under optimized growth conditions, a sheet resistance of 15.2 /, average transmittance above 89% in the green range, and a root mean square roughness of 0.375 nm were obtained, even for the IZO anode film grown in a pure Ar ambient without the addition of oxygen as a reactive gas. All of the IZO anode films had an amorphous structure regardless of the rf power and the working pressure due to the low substrate temperature of 50°C and the structural stability of the amorphous IZO films. In addition, an X-ray photoelectron spectroscopy depth profile obtained for the IZO/PES showed no obvious evidence of interfacial reactions between the IZO anode and the PES substrate, except for some indiffusion of oxygen atoms from the IZO anode. Furthermore, the current-voltage-luminance of the flexible OLEDs fabricated on IZO anode was found to be critically dependent on the sheet resistance of the IZO anode. ; This work was supported by a Korea Research Foundation grant funded by the Korean Government (MOEHRD: Basic Research Promotion Fund)(KRF-2006-003-D00243) and the Ministry of Commerce, Industry and Energy.

The authors report the enhancement of hole injection using an indium tin oxide (ITO) anode covered with ultraviolet (UV) ozone-treated Ag nanodots for fac tris (2-phenylpyridine) iridium Ir(ppy)3-doped phosphorescent organic light-emitting diodes (OLEDs). X-ray photoelectron spectroscopy and UV-visible spectrometer analysis exhibit that UV-ozone treatment of the Ag nanodots dispersed on the ITO anode leads to formation of Ag2O nanodots with high work function and high transparency. Phosphorescent OLEDs fabricated on the Ag2O nanodot-dispersed ITO anode showed a lower turn-on voltage and higher luminescence than those of OLEDs prepared with a commercial ITO anode. It was thought that, as Ag nanodots changed to Ag2O nanodots by UV-ozone treatment, the decrease of the energy barrier height led to the enhancement of hole injection in the phosphorescent OLEDs. ; This work was supported by Korea Research Foundation grant funded by Korean Government (MOEHRD: Basic Research Promotion Fund)(KRF-2006-003-D00243) and Ministry of Commerce, Industry, and Energy.

The preparation and characteristics of a transparent conducting indium zinc tin oxide (IZTO) anode for highly efficient phosphorescent organic light emitting diodes (OLEDs) is described. The resistivity and transmittance of the IZTO anode are comparable to reference In2O3 (ITO) anode films even though it was prepared at room temperature. In addition, the work function of the ozone-treated amorphous IZTO anode (5.12±0.02 eV) is much higher than that of ozone-treated reference ITO anodes (4.94±0.02 eV). The current-voltage-luminance characteristics and efficiencies of OLEDs prepared on the IZTO anode are critically dependent on the sheet resistance of the IZTO anode. Furthermore, both the quantum efficiency and power efficiency of the OLED fabricated on the amorphous IZTO anode are much higher than those of an OLED with the reference ITO anode due to the higher work function of the IZTO anode than those of conventional ITO anode. This indicates that IZTO is an alternative material for conventional ITO anodes used in OLEDs and flexible displays. ; This work was supported by a Korea Research Foundation Grant funded by the Korea Government MOEHRD: Basic Research Promotion Fund grant no. KRF-2006-331-D00243 and the Ministry of Commerce, Industry, and Energy.

Iridium complexes containing cyclometalated 2-cyclohexenylpyridine derivatives with rigid and bulky cyclohexene units are synthesized, and found to be highly efficient materials in EL devices (see figure). Devices based on these iridium complexes emit yellowish- green light with the very high external quantum efficiency of 18.7%. ; This work was supported by a Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (KRF-2006-005- D00251), partially supported by the Strategic Technology Development Program (10030814), and partially supported by the Ministry of Commerce

Highly efficient deep-blue fluorescent materials based on phenylquinoline-carbazole derivatives (PhQ-CVz, MeO-PhQ-CVz, and CN-PhQ-CVz) are synthesized for organic light-emitting diodes (OLEDs). The materials form high-quality amorphous thin films by thermal evaporation and the energy levels can be easily adjusted by the introduction of different electron-donating and electron-withdrawing groups on carbazoylphenylquinoline. Non-doped deep-blue OLEDs that use PhQ-CVz as the emitter show bright emission (Commission Internationale de L'Éclairage (CIE) coordinates, x = 0.156, y = 0.093) with an external quantum efficiency of 2.45%. Furthermore, the material works as an excellent host material for 4,4-bis(9-ethyl-3-carbazovinylene)-1,1-biphenyl dopant to get high-performance OLEDs with excellent deep-blue CIE coordinates (x = 0.155, y = 0.157), high power efficiency (5.98 lm W-1), and high external quantum efficiency (5.22%). ; This research was supported by a Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MEST) (No. M10600000157-06J0000-15710) and the University IT Research Center (ITRC) Project of the Ministry of Knowledge Economy.