Study on hybrid blue organic light emitting diodes with step controlled doping profiles in phosphorescent emitting layer

Lee, Bo Mi,Kim, Jinwook,Yun, Geum Jae,Kim, Woo Young,Mascher, Peter Elsevier 2018 Optical materials Vol.86 No.-

<P><B>Abstract</B></P> <P>We have designed blue organic light emitting diodes (OLEDs) consisting of fluorescent and phosphorescent emitters whose phosphorescent emitting layers have three step-controlled doping profiles of 0, 4 and 8%. The different doping profiles determined the characteristics of electroluminescent and fluorescent intensity variation under various voltages. Also, it was found that emission channels separated by the non-doped region enhanced fluorescent emission. The phosphorescent doping concentration adjacent to the fluorescent emitting layer is strongly related to device efficiency and the location of the non-doped region, particularly, affected the electrical and optical characteristics of the blue OLEDs due to the hole transport type of the host material. Placing the region on the anode side had the effect of widening the hole transport region, leading to higher current density. Based on this effect, the device with the regularly stepwise doping concentration (0-4-8%) showed high current density and luminance but the phosphorescent emission was dominant. The lowest efficiency roll-off was observed from the device containing the separated emission channels for fluorescence and phosphorescence by the non-doped region, which gave rise to relatively stronger fluorescent emission.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Both fluorescent and phosphorescent emitters are used and the phosphorescent emitter is step doped of 0, 4 and 8 %. </LI> <LI> The non-doped region (0% FIrpic) influenced electrical and optical properties of blue OLEDs. </LI> <LI> The different doping profiles vary the device efficiency and fluorescent intensity. </LI> </UL> </P>

Exciplex hosts for blue phosphorescent organic light-emitting diodes

Mina Jung,Jun Yeob Lee 한국정보디스플레이학회 2020 Journal of information display Vol.21 No.1

The host material of organic light-emitting diodes (OLEDs) has been advanced from a single host to a mixed host for high efficiency and long lifetime. Several types of mixed host have been reported in the literature, but the exciplex host has been popular as the mixed host of OLEDs. The exciplex host has been developed mostly for red and green phosphorescent OLEDs, and has upgraded device performances, but it is difficult to develop the exciplex host for blue phosphorescent OLEDs. Recently, several works demonstrated the potential of the exciplex host for blue phosphorescent OLEDs. In this paper, the exciplex host for blue OLEDs is reviewed, and its prospects are presented.

The New Iridium(III) Pyridyltetrazolate Complexes for Blue Phosphorescence

Lee, Hyun-Shin,Ha, Yunkyoung TaylorFrancis 2009 Molecular Crystals and Liquid Crystals Vol.504 No.1

<P> A series of new blue-phosphorescent iridium complexes containing phenypyridine (ppy) derivatives and pyridyltetrazole were synthesized and their photophysical and electroluminescent properties were investigated. In the complex, the phenyl moiety which is mostly the highest occupied molecular orbital (HOMO) site was modified with the electron-withdrawing groups F and CF3. By doing so, the emission maxima were expected to shift hypsochromically due to the HOMO level decrease. Furthermore, addition of the modest electron donating group, CH3, to the pyridyl moiety in the ligand could slight raise the lowest unoccupied molecular orbital (LUMO) level of the complex. Therefore, the energy gap increase of the main ligands, phenylpyridine derivatives, might lead to blue emission of their iridium complexes. Previously reported pyridyltetrazole, an ancillary ligand, were also introduced to the iridium complexes for efficient blue phosphorescence and charge balance. The complexes prepared herein exhibited the blue emission at 467 and 486 nm with a shoulder peak at the longer wavelengths, respectively. We also investigated the luminescence properties of the complexes in a polymer film of PMMA (poly(methylmetacrylate)) for their application to the solution process. The photoemission of the complex in PMMA showed similar pattern with that of the complex itself.</P>

Tetrahedral Silicon-based TriPhenylAmine(TPA) as Novel Hole Transporting Materials for High Thermal Stability and High Efficient Phosphorescent OLEDs

손미랑,윤보선,강상욱,손호진 한국공업화학회 2016 한국공업화학회 연구논문 초록집 Vol.2016 No.1

A series of modified 4,4′-Cyclohexylidenebis[N,N-bis(4-methylphenyl) benzenamine] (TAPC), TAPC, SiTAPC, 2MeSi(TPA)₂, MeSi(TPA)₃ derivative have been tested as Hole-Transport Material for deep blue phosphorescent OLEDs. Systematic investigations of their thermal-, photophysical-, and Hole-transporting (HT) properties were carried out. Lowtemperature photoluminiscenec spectra indicate that all the prepared TAPC moieties maintained high triplet energy states up to 2.9 eV owing to the suppression of electron delocalization by silicon centre. All prepared compounds have high triplet energy levels, which is compatible with the energy level of blue phosphorescent emitting layer in blue OLED device. TDDFT calculations were also performed to figure out their frontier orbital distributions and their transition states. In currentvoltage (I-V) measurement (hole only devices (HOD)) to estimate their hole mobilities, the MeSi(TPA)₃ showed higher current density than the other analogs.

BCP 두께가 청잭 인광 OLED의 전기 및 광학적 특성에 미치는 영향

서유석,문대규,Seo, Yu-Seok,Moon, Dae-Gyu 한국전기전자재료학회 2009 전기전자재료학회논문지 Vol.22 No.9

We have fabricated simple triple-layer blue-emitting phosphorescent organic light emitting diodes (OLEDs) using different thicknesses (25 and 55 nm) of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) electron transport layers. 1,1-bis[4-bis (4-methylphenyl)- aminophenyllcyclohexane (TAPC), bis[(4,6-di-fluorophenyl)-pyridinate-$N,C^{2'}$]picolinate (FIrpic) and N,N' -dicarbazolyl-3,5-benzene (mCP) were used as hole transport, blue guest and host materials, respectively. The driving voltage, electroluminescence (EL) efficiency and emission characteristics of devices were investigated. The maximum EL efficiency was 20 cd/A in the device with 55 nm BCP layer, which efficiency was about 33% higher than the device with 25 nm BCP layer. The higher efficiency in the 55 nm BCP device resulted from the enhanced electron-hole balance. In the EL spectrum of blue phosphorescent OLED with BCP layer, the relative intensity between 470 and 500 nm peaks was related to the location of emission zone.

The Correlation between Structure and Physical Properties of Soluble Host for Blue Phosphorescent OLED

최희재,김범석,김오영,진병두,이칠원 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.12

Blue phosphorescent organic light-emitting diodes (OLED) were prepared with the host materials designed for solution process. 3,5-di(9$H$-carbazol-9-yl)-1,1$'$:2$'$,1$''$-terphenyl and 3,5-di(9$H$-carbazol-9-yl)-1,1$'$:2$'$,1$''$:2$''$,1$'''$-quarterphenyl were synthesized to investigate the relationship among the molecular structure, solubility, and optoelectronic properties. These materials used 1,3-bis(carbazole-9-yl)benzene as the core structure and $ortho$-biphenyl or $ortho$-terphenyl was introduced into the benzene ring between the two carbazole moieties of 1,3-bis(carbazole-9-yl)benzene for the purpose of reducing symmetry and planarity of the molecules. Design concept in this study is unique in terms of the improvement of solubility without the inclusion of an alkyl group, which is generally disadvantageous for OLED stability. The prepared materials, especially with $ortho$-terphenyl, showed sufficiently better solubility, thermal stability, and high triplet energy even though the extended state of benzene rings. Therefore, it can be employed as a suitable host design concept capable of forming a solution-processed emitting layer having an improved stability for a fabrication of blue phosphorescent OLEDs.

Drastic drop of external quantum efficiency at liquid nitrogen temperature in a bilayer blue phosphorescent organic light-emitting device

Ha, Mi-Young,Park, Da-Young,Lee, Min-Jae,Choi, Seung-Jung,Jung, Jae-Hoon,Moon, Dae-Gyu Elsevier Sequoia 2016 Synthetic metals Vol.217 No.-

<P><B>Abstract</B></P> <P>We have investigated substantial drop of external quantum efficiency (EQE) at liquid nitrogen temperature in a bilayer blue phosphorescent organic light emitting device with a structure of ITO/TAPC:FIrpic/TAZ/LiF/Al, where TAPC, FIrpic, and TAZ represent 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane, iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C<SUP>2′</SUP>]picolinate, and 3-(biphenyl-4-yl)-4-phenyl-5-(4-tert-butyl-phenyl)-1,2,4-triazole, respectively. The device exhibits a high EQE of 17.2% at room temperature although it has a simple bilayer structure. However, the quantum efficiency drops drastically to 0.8% at liquid nitrogen temperature. We studied this drastic drop of EQE in viewpoints of carrier conduction, carrier recombination, photoluminescence quantum efficiency, and energy transfer.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We developed highly efficient bilayer blue phosphorescent OLEDs. </LI> <LI> External quantum efficiency (EQE) was 17.2% at room temperature. </LI> <LI> EQE drastically drops to 0.8% at liquid nitrogen temperature. </LI> <LI> The drop of EQE was critically dependent on the TAZ layer. </LI> </UL> </P>

전자수송층이 청색 인광 OLED의 전기 및 광학적 특성에 미치는 영향

서원규,문대규,Suh, Won-Gyu,Moon, Dae-Gyu 한국전기전자재료학회 2009 전기전자재료학회논문지 Vol.22 No.4

We have developed blue-emitting phosphorescent organic light emitting diodes (OLEDs) using 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and tris (8-quinolinolato)aluminum ($Alq_3$) electron transport layers. As blue dopant and host materials, bis[(4,6-di-fluorophenyl)-pyridinate-N,C2']picolinate (FIrpic) and N,N'-dicarbazolyl-3,5-benzene (mCP) were used, respectively. The driving voltage, current efficiency and emission characteristics of devices were investigated. While the driving voltage was about $1{\sim}2$ V lower in the device with an $Alq_3$ layer, the current efficiency was about 66 % higher in the device with BCP electron transport layer. the blue phosphorescent OLED with BCP layer exhibited higher purity of color, resulting from a relatively weak electroluminescence intensity at 500 nm.

Design strategy for higher energy of exciplex in blue phosphorescent organic light-emitting diodes

최경현,이하림,이준엽 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

New electron type host, 2,8-bis(4,6-bis(3,5-di-tert-butylphenyl)-1,3,5-triazin-2-yl)dibenzo[b,d]furan (DBFtTrz) was synthesized to make intermolecular interaction weaker by substituting tert-butyl group in triazine moiety. In photoluminescence (PL) measurement, the t-butyl substituted electron type host showed blue-shifted emission in exciplex formation both singlet and triplet energy compared with n-type host which has no t-butyl substitution. In device, the new synthesized n-type host pair showed higher external quantum efficiency (17.3%).

발광층 두께가 삼층 구조 청색 인광 OLED의 효율 특성에 미치는 영향

서유석,문대규,Seo, Yu-Seok,Moon, Dae-Gyu 한국전기전자재료학회 2010 전기전자재료학회논문지 Vol.23 No.2

We have fabricated simple triple-layer blue-emitting phosphorescent organic light emitting diodes (OLEDs) using different thicknesses of N,N'-dicarbazolyl-3,5-benzene (mCP) host layers doped with bis[(4,6-di-fluorophenyl)-pyridinate-N,$C^{2'}$]picolmate (FIrpic) guest materials. The thicknesses of mCP:FIrpic layers were 5, 10, and 30 nm. Driving voltage, current and power efficiencies were investigated. The current efficiency was higher in the 10 nm thick mCP:FIrpic device, resulting from the better electron-hole balance. The device with 10 nm mCP:FIrpic layer exhibited the maximum current efficiency of 22.5 cd/A and power efficiency of 7.4 lm/W at a luminance of 1000 cd/$m^2$.