Blue Emission Color Control by Co-Deposition Method in Organic Light Emitting Diodes

9,10-bis(3′′,5′′-diphenylbiphenyl-4′-yl)anthracene (TAT) and 4-(1′-(3′,5′-diphenylbiphenyl-4-yl)anthracen-9-yl)-N,N-diphenylaniline (TATa) which have electroluminescence (EL) maximum values of 441nm and 469 nm were used blue emitting materials in organic light emitting diodes (OLED). OLED devices were fabricated and characterized by co-deposited emitters of TAT and TATa with different ratios. C.I.E. values of the devices using TAT and TATa were changed from (0.148, 0.081) to (0.139, 0.194).     

New Emitting Materials Based on HTL Moiety with High Hole Mobility for OLEDs

New green emitting compounds based on tris(N-methylindolo)benzene (NMT), anthracene and pyrene were synthesized. NMT-An and NMT-Py were used as an emitting layer in OLED device to examine emitting property. OLED device containing NMT-An emitting layer and conventional hole transporting layer (HTL) of NPB was found to exhibit better characteristics compared to NMT-Py. And that device showed maximum EL emission at 502 nm and 550 nm, CIE coordinates (0.38, 0.48), and a luminance efficiency of 2.06 cd/A. Also when NMT and NMT-An were used as a HTL instead of NPB, the device including NMT-An emitter showed 2.67 cd/A and 2.29 cd/A in luminance efficiency.     

Efficient deep blue organic light emitting diodes based on [2,7,7,13,13-pentamethyl-9-(10-phenylanthracen-9-yl)-7,13-dihydrobenzo[5,6]-s-indaceno[1,2-g]quinoline] derivatives

Abstract

In this study, as the ongoing effort to develop efficient blue OLEDs, two deep blue emitters based on indenoquinoline-substituted anthracene derivatives have been synthesized and characterized. Multilayer organic light emitting diodes were fabricated with the following sequence: indium-tin-oxide (ITO)/4,4’,4’’-tris[2-naphthyl(phenyl)amino (2-TNATA)/4,4’-bis(N-(1-naphthyl)-N-phenylamino) biphenyl (NPB)/Blue emitting materials/Bathophenanthroline (Bphen)/lithium quinolate (Liq)/Al. All the devices showed efficient blue emissions. Particularly, a device using ‘2,7,7,13,13-pentamethyl-9-(10-phenylanthracen-9-yl)?7,13-dihydrobenzo[5,6]-s-indaceno[1,2-g] quinoline’ as an emitter showed a maximum external quantum efficiency (EQE) of 4.92% with the Commission Internationale De L’Énclairage (CIE) coordinates of (0.15, 0.10) at 8.0?V.     

Efficient Charge Balance of Green Organic Light Emitting Diodes Using Mixed Charge Transporting Materials as the Host

The mixed layer for an emitting layer (EML) consists of two materials 4,4′,4′′-tris(N-carbazolyl)-triphenylamine (TCTA) and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) without host material. A series of EML structures were fabricated with three types of single mixed layers (mixing ratio 2:1, 1:2) and double mixed layers (mixing ratio 2:1/1:2), and the EML of using double mixed layer was optimized. The maximum luminous efficiency (LE) and quantum efficiency (QE) were 62.07 cd/A, 18.92%, respectively. Moreover, the roll-off ratio of LE was 20.42% at 20,000 cd/m². Interestingly, this result shows the roll-off ratio was reduced roughly 50% compared to the reference device.     

Synthesis and Property of New Blue Emitting Materials with Bulky Side Group

Two emitting compounds, 9,10-bis-[1,1′;3′,1′′]terphenyl-5′-yl-1,5-di-o-tolyl-anthracene [TP-DTA-TP] and 9,10-bis-phenyl[1,1′;3′,1′′]triphenyl-5′-yl-1,5-di-o-tolyl-anthracene [TPB-DTA-TPB] based on new twisted core moiety were synthesized through boration, Suzuki reaction, and Sandmeyer reactions. EL performance was improved by varying the chemical structure of the side group. Physical properties such as optical, electrochemical, and electroluminescent properties were investigated. Synthesized compounds were used as an EML in OLED device: ITO / 2-TNATA (60nm) / NPB (15nm)/ TP-DTA-TP or TPB-DTA-TPB (35 nm) / Alq3 (20nm) / LiF (1nm) / Al (200nm). It was found that TPB-DTA-TPB showed higher luminance efficiency and better C.I.E. value than TP-DTA-TP device.     

Liquid crystal properties of dimers having two identical terminal units and a central oxyethylene spacers

ABSTRACT

In this research, we designed and synthesized blue emitting materials based on aminofluorene-substituted pyrene derivatives. Organic light-emitting diodes (OLEDs) devices using these materials were fabricated in the following sequence; ITO/N,N′-diphenyl-N,N′-(2-napthyl)-(1,1′-phenyl)-4,4′-diamine (NPB) (500 Å)/Blue emitters 1 or 2 (300 Å)/4,7-diphenyl-1,10-phenanthroline (BPhen) (300 Å)/lithium quinolate (Liq) (20 Å)/Al (1000 Å). These devices showed efficient blue emissions. Particularly, a device A using 7-(1-(2-(diphenylamino)-9,9-diethyl-9H-fluoren-7-yl)pyren-6-yl)-9,9-diethyl-N,N-diphenyl-9H-fluoren-2-amine (1) as blue emitter exhibited luminous efficiency, power efficiency, and external quantum efficiency of 2.20 cd/A, 0.80 lm/W, 1.62% at 100 mA/cm², respectively, with Commission Internationale d’Énclairage (CIE) coordinates of (0.17, 0.24) at 8.0 V.     

Organic Light-Emitting Diodes based on Benzo[q]quinoline Derivatives

Abstract

In this study, we synthesized two emitting materials based on benzo[q]quinoline derivatives. OLED devices using these materials were facricated in the following sequence;ITO(180nm)/4,4',4''-Tris[2-naphthyl(phenyl)amino]triphenylamine(2-TNATA)(30nm)/N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine(NPB)(20nm)/Emitting materials(30nm)/4,7-diphenyl-1,10-phenanthroline (Bphen)(30nm)/Liq(2nm)/Al(100nm). Particularly, a device using 2,4-di(naphtalene-1-yl)benzo[q]quinoline as an emitter exhibited the efficient emission with a luminous efficiency, a power efficiency, and exteranl quantum efficiency of, and the CIE coordinates of 2.91cd/A, 0.99lm/W, 0.90% at 20mA/cm², and (0.33, 0.55) at 1000cd/m², respectively. Interestingly, emissions from electromers and electroplexes were shown to be crucial role in electroluminescences from benzo[q]quinoline derivatives     

Synthesis and Properties of New Imidazole Derivatives Including Various Chromophore for OLEDs

Abstract

Two new blue compounds were successfully synthesized by introducing phenanthroimidazole group as a side group into pyrene, a chromophore with good luminous efficiency: 1-(4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)-2-(pyren-1-yl)-1H-phenanthro[9,10-d]imidazole (NA-PPI) and 1-(4'-(9H-carbazol-9-yl)-[1,1'-biphenyl]-4-yl)-2-(pyren-1-yl)-1H-phenanthro[9,10-d]imidazole (CP-PPI). The optical and electroluminescence properties of newly synthesized materials were measured. Both materials emit blue or sky-blue photoluminescence in the film state and have a high PLQY value of over 80% in solution state. The synthesized materials were applied as EML in non-doped devices, and high efficiency of 3.51?cd/A and EQE of 2.39% in CP-PPI device were achieved.     

Synthesis and Electroluminescence Property of New Hexaphenyl Benzene Derivatives Including Emitting Materials for OLED

Three new emitting compounds of 5P-VCB, 5P-VAn and 5P-VPy for OLED based on hexaphenylbenzene moiety were synthesized. Physical properties by the change of the substitution groups of the synthesized materials were systematically examined. Photoluminescence spectrum of the synthesized materials showed maximum emitting wavelengths of about 420～487 nm in solution state and 452～488 nm in film state, indicating blue emission color. OLED devices were fabricated by the synthesized compounds using vacuum deposition process as an emitting layer. Current efficiencies and CIE values of 5P-VCB, 5P-VAn and 5P-VPy were 1.76, 0.38 and 7.91 cd/A and (0.15, 0.07), (0.20, 0.31) and (0.20, 0.36), respectively.     

Synthesis and Characterization of Violet Light Emitting Polymer based on Fluorene and Dimethylsilane

New fluorene based light emitting polymer, poly[(4-(9,9-didecyl-9H-fluoren-2-yl) phenyl)dimethyl(phenyl)silane] (PFDPS), was synthesized by palladium-catalzed Suzuki coupling reaction. The obtained copolymer was characterized by ¹H-NMR, and IR-spectroscopy. The polymer showed good solubility in common organic solvents and weight average molecular weight of 16,300 with polydispersity index of 1.4. The maximum photoluminescence of the solution and film of the polymer was observed at 392 nm and 410 nm, respectively.

The double-layered device with the configuration, ITO/PEDOT/PFDPS/LiF/Al structure has a turn-on voltage at about 5.5 V and maximum brightness of 9.40 cd/m², and emitted violet light at 414 nm.     

Blue electroluminescent materials based on indeno[1,2-a]arene derivatives for Organic Light-Emitting Diodes

Abstract

In this study, as a continuous effort for searching efficient blue-emitting materials, we designed and synthesized materials based on indeno[1,2-a]arene. OLED devices using these materials were fabricated in the following sequence; ITO (180?nm)/N,N'-diphenyl-N,N'-(2-napthyl)-(1,1'-phenyl)-4,4'-diamine (NPB) (50?nm)/emitting materials (30?nm)/4,7-diphenyl-1,10-phenanthroline (Bphen) (30?nm)/Liq/Al (2/100?nm). Particularly, a device using 7,7-dimethyl-7H-indeno[1,2-a]pyrene as emitter showed maximum values of luminous efficiency, power efficiency, and external quantum efficiency of 1.10?cd/A, 0.49?lm/W, 1.47% at 20?mA/cm², respectively with CIE (x,y) coordinates of (0.15, 0.08) at 6.0V.     

Synthesis and property of diazocine derivatives substituted with imidazole in various positions

ABSTRACT

TIACA-I, TIACA-II were synthesized by changing the substitution position of the imidazole group in the diazocine core. TIACA-I, TIACA-II in the film state showed absorption in the range of 354 to 392 nm and exhibited blue photoluminescence (PL) emissions at 448 and 462 nm, respectively. The PL wavelength of TIACA-II is red-shifted by 14 nm than that of TIACA-I due to the electron-donating intensity depending on the position of the imidazole group. The use of TIACA-II in a non-doped OLED device resulted in blue emission with current efficiency of 2.84 cd/A and CIE of (0.15, 0.18).     

Synthesis and electroluminescent properties of new diazocine derivatives

ABSTRACT

DAPCz and DANaPCz have been successfully synthesized and characterized. DAPCz and DANaPCz in film state showed absorption in the range of 322 to 345 nm wavelength and exhibited blue photoluminescence (PL) emission peaks at 428 and 425 nm. PL wavelength of DAPCz is red-shifted by 3 nm than that of DANaPCz, which is due to the carbazole electron donating group of DAPCz. The use of DAPCz in a non-doped OLED device resulted in blue emission with current efficiency of 1.01 cd/A and C.I.E. of (0.26, 0.37).     

Highly Luminescent Red Phosphorescent OLED with Interfacial Layers for Hole Transport and Electron Injection

Four kinds of red phosphorescent organic light-emitting devices were fabricated and compared to investigate the effect of interfacial layers for hole transport and electron injection. 1 nm-thick LiF in the device A and C and 1 nm-thick Cs₂CO₃ in the device B and D were deposited as an electron injection layer between the anode and the electron transport layer, and 5 nm-thick layer of dipyrazion[2,3-f:2′,2′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile[HATCN] was inserted as a hole transport interfacial layer between the hole injection layer and the hole transport layer only in the device C and D. Under a luminance of 1000 cd/m², the power efficiencies were 7.6 lm/W and 8.5 lm/W in the device A and B, and 8.6 lm/W and 13.4 lm/W in the device C and D. The quantum efficiency of the device D was 15.8% under 1000 cd/m² which was somewhat lower than those of the device A and C, but a little higher than that of the device B. The luminance of the device D was much higher than those of the other devices at a given votage. The luminance of the device D at 7 V was 23,710 cd/m², which was 13.0, 3.4, and 4.0 times higher than those of the device A, B, and C at the same voltage, respectively.     

Theoretical Design Study on the Electronic Structures and Phosphorescent Properties of Four Iridium(III) Complexes

The geometry structures, electronic structures, absorption, and phosphorescent properties of four Ir(III) complexes have been investigated using the density functional method. Calculations of ionization potential (IP) and electron affinity (EA) were used to evaluate the injection abilities of holes and electrons into these complexes. The result also indicates that the –CF₃ substituent group on the ligand not only change the character of transition but affect the rate and balance of charge transfer. The lowest energy absorption wavelengths are located at 428 nm for 1a, 446 nm for 1b, 385 nm for 2a, and 399 nm for 2b, respectively, in good agreement with the energy gap (ΔE_L-H) trend because the HOMO–LUMO transition configurations are predominantly responsible for the S₀→S₁ transition. 2b has the 433 nm blue emission, which might be a potential candidate for blue emitters in phosphorescent dopant emitters in organic light emitting diodes (OLEDs). The study could provide constructive information for designing novel OLEDs materials in the future.

[Supplemental materials are available for this article. Go to the publisher's online edition of Molecular Crystals and Liquid Crystals to view the free supplemental file.]     

高效氟代联蒽类深蓝光材料的合成及OLED性能

为了开发新型多功能的蓝光电致发光材料与器件,设计并合成了一系列氟取代联蒽类材料(BAnFs),通过改变吸电子基团的取代模式,进而调节其光物理性能、热稳定性和能级.以CBP为主体、BAnFs为掺杂的器件表现出高效的深蓝光发光性能,对应的色坐标为CIE (0.15, 0.08),特别是对BAn-(3,5)-CF3器件的电流效率为3.05 cd/A,最大外量子效率(EQE)高达5.02;.同时BAnFs材料可作为高性能的蓝光主体材料,其EQE为3.56;~5.43;.因此,BAnFs可作为新型高性能的多功能蓝光发光材料.     

Comparison Study of Phenylquinoline-based Iridium(III) Complexes for Solution Processable Phosphorescent Organic Light-Emitting Diodes by PEDOT:PSS and Graphene Oxide as a Hole Transport Layer

Electroluminescent (EL) properties of Ir(III) complex, [(2,4-diphenylquinoli-ne)]₂Iridium picolinic acid N-oxide [(DPQ)₂Ir(pic-N-O)] were investigated using PEDOT:PSS and reduced graphene oxide (rGO) as a hole transport layer for solution processable phosphorescent organic light-emitting diodes (PhOLEDs). High performance solution-processable PhOLED with PEDOT:PSS and (DPQ)₂Ir(pic-N-O) (8 wt%) doped CBP:TPD:PBD (8:56:12) host emission layer were fabricated to give a high luminance efficiency (LE) of 26.9 cd/A, equivelent to an external quantum efficiency (EQE) of 14.2%. The corresponding PhOLED with rGO as a hole transport layer exhibited the maximum brightness and LE of 13540 cd/m² and 16.8 cd/A, respectively. The utilization of the solution processable rGO thin films as the hole transport layer offered the great potential to the fabrication of solution processable PhOLEDs.     

The nature of the electrical conduction and light emitting efficiency in organic semiconductors layers: The case of [m-MTDATA] – [NPB] – Alq3 OLED

In this work, a detailed study on the influence of different layers in an Alq3 [aluminium-tris(8-hydroxyquinoline)] based OLED is made. Two hole transport layers have been used: m-MTDATA [4,4′,4″-tris (3-methyl-phenylphenylamino) triphenylamine] and NPB [N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4″-diamine]. It is found that the efficiency (at 520 nm) can increase up to one order of magnitude when we consider a three layer device instead of a conventional two layer. The driving voltage decreases in the three layer device, but the output electroluminescence spectra (in green spectral region) tend to be broaden towards high energies. The current–voltage behavior follows a space charge limited current behavior. The influence of the traps states and/or a Poole-Frenkel like field mobility dependence is discussed. The electroluminescence data fit to a large green band (one main green band and a small orange band) and for the three layer device a small blue band appears. Finally, a model involving an individual layer contribution with the corresponding trap levels is proposed.     

Strain variation in p-GaN by different spacer layers in the light emitting diodes and their microstructural and emission behaviors

InGaN/GaN multiple quantum well-based blue light emitting diodes (LEDs) with different spacer layer structures were grown by metalorganic chemical vapor deposition. Fast-Fourier-transformed high-resolution transmission electron microscopy was used to determine the influence of the strain status in the spacer layer on Mg distribution and device performance. A comparison of the (1 1¯ 0 0) planar distance showed that the high-temperature grown InGaN layer in the spacer had a high level of stored strain. This led to the formation of a continuous facet contrast induced by Mg segregation in the p-layer, which was responsible for the deterioration of the electroluminescence performance of the LEDs. These results show that the delicate control of stored strain in nitride films is important for improving the device performance.     

A BODIPY-based highly emissive dye with thiophene-based branch harvesting the light

ABSTRACT

A novel BODIPY-based dye with highly emissive character was configured by Sonogashira coupling and routinely characterized by NMR and MS technology. The emission of dye was investigated in solution/film/solid and shows intensive emission. In solution, the emission peak appeared around 510 nm with little influence by the polar environment. The terthiophene plays an effective antenna effect, harvesting the light and transferring the energy to BODIPY. The pseudo Stoke's shift enlarged to ～170 nm in solution. In film, the emission peak shifted to 563 nm in polycarbonate matrix. And it shifted further to 585 nm in solid due to the highly twisted structure, which avoided closely regular-tight packing. The dye rendered an intense fluorescence, good optothermal stability, and high fluorescence quantum yield (0.55). The solid emission showed highly red emission with Commission Internationale de L'Eclairage (CIE) coordinates of (X = 0.69, Y = 0.31). Thus, the synthesized dye is idea candidate for emitting materials.