Modified 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetra-methyljulolidyl-9-enyl)-4H-pyran-containing red fluorescent emitters for efficient organic light-emitting diodes

Efficient red fluorescent compounds Red 1 and Red 2 based on bulky bicyclo[2,2,2]octane groups in the pyran moiety and tert-butyl or isopropyl group in the julolidine moiety of the 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetra-methyljulolidyl-9-enyl)-4H-pyran (DCJTB) skeleton were synthesized and characterized. As red-emitting dopants in an Alq₃ single-host emitting system, Red 1 and Red 2 exhibited improved color purity and enhanced luminous efficiency compared to DCJTB. Moreover, a device using Red 1 as a dopant in a rubrene-Alq₃ co-host emitting system exhibited improved electroluminescence performance with a luminous efficiency and power efficiency of 6.89 cd/A and 3.09 lm/W at 20 mA/cm², respectively, and CIE x,y coordinates of (x = 0.64,y = 0.36) at 7.0 V, approaching saturated red emission.     

Synthesis and electroluminescent properties of blue-emitting t-butylated bis(diarylaminoaryl)anthracenes for OLEDs

A new series of blue fluorescent emitters based on t-butylated bis(diarylaminoaryl) anthracenes were synthesized and their electroluminescent properties investigated. Into these blue materials, t-butyl groups were introduced to both prevent molecular aggregation between the blue emitters through steric hindrance and reduce self-quenching. As such, this would contribute to overall improvement in OLED efficiency. To explore the electroluminescent properties of these materials, multilayered OLEDs were fabricated into a device structure of: ITO/NPB(50 nm)/blue emitters doped in ADN(30 nm)/Alq₃(20 nm)/Liq(2 nm)/Al(100 nm). All devices showed efficient blue emissions. In particular, one device exhibited highly efficient sky blue emissions with a maximum luminance of 11,060 cd/m² at 12.0 V and respective luminous and power efficiencies of 6.59 cd/A and 2.58 lm/W at 20 mA/cm². The peak wavelength of the electroluminescence was 468 nm with CIEx,y coordinates of (0.159, 0.198) at 12.0 V. In addition, a deep blue device with CIEx,y coordinates of (0.159, 0.151) at 12.0 V showed a luminous efficiency of 4.2 cd/A and power efficiency of 1.66 lm/W at 20 mA/cm².     

t-Butyl group-substituted triphenylamine-containing orange-red fluorescent emitters for organic light-emitting diodes

Efficient orange-red fluorescent compounds, 4-(dicyanomethylene)-2-adamantyl-6-(4-(N-(4-tert-butylphenyl)-N-(3,5-di-tert-butylphenyl)amino)benzene)vinyl-4H-pyran (DCATP) and 2,6-bis[4-(N-(4-tert-butylphenyl)-N-(3,5-di-tert-butylphenyl)amino)benzene]vinyl-4-(dicyanomethylene)-4H-pyran (BDCTP) containing the tert-butylated triphenylamine in donor moieties, were synthesized and characterized. In these red emitters, bulky groups, such as t-butyl group and adamantane were introduced to increase the steric hindrance between the red emitters. In particular, an efficient orange-red device containing the emitter DCATP as a dopant showed a luminous and power efficiency of 6.87 cd/A and 2.70 lm/W, respectively, at 20 mA/cm² with the CIE coordinates of (0.48, 0.50) at 7.0 V. In addition, an efficient red organic light-emitting diode using BDCTP as a dopant exhibited a luminous and power efficiency of 2.30 cd/A and 1.31 lm/W, respectively, at 20 mA/cm² and CIE coordinates of (0.61, 0.39).     

Synthesis and electrophosphorescent properties of iridium complexes based on 2-fluorenylquinoline derivatives

A series of cyclometalated iridium complexes with 2-fluorenylquinoline derivative ligands were synthesized and their photophysical and electroluminescent properties examined using multilayered, organic light-emitting diodes fabricated with the complexes as dopant materials. In the device containing the complex 3 dopant, the maximum luminance was 20,200 cd/m² at 14 V, the luminous and power efficiencies were 14.1 cd/A and 11.0 lm/W, respectively, and the CIE coordinates were (0.65, 0.35) which were close to saturated red emission.     

Highly efficient red phosphorescent Ir(III) complexes for organic light- emitting diodes based on aryl(6-arylpyridin-3-yl)methanone ligands

A series of phosphorescent Ir(III) complexes 1-4 were synthesized based on aryl(6-arylpyridin-3-yl)methanone ligands, and their photophysical and electroluminescent properties were characterized. Multilayer devices with the configuration, Indium tin oxide/4,4′,4″-tris(N-(naphthalene-2-yl)-N-phenyl-amino)triphenylamine (60 nm)/4,4′-bis(N-(1-naphthyl)-N-phenylamino)biphenyl (20 nm)/Ir(III) complexes doped in N,N′-dicarbazolyl-4,4′-biphenyl (30 nm, 8%)/2,9-dimethyl-4,7-diphenyl-phenathroline (10 nm)/tris(8-hydroxyquinoline)-aluminum (20 nm)/lithium quinolate (2 nm)/ Al (100 nm), were fabricated. Among these, the device employing complex 2 as a dopant exhibited efficient red emission with a maximum luminance, luminous efficiency, power efficiency and quantum efficiency of 16200 cd/m² at 14.0 V, 12.20 cd/A at 20 mA/cm², 4.26 lm/W and 9.26% at 20 mA/cm², respectively, with Commission Internationale de l'Énclairage coordinates of (0.63, 0.37) at 12.0 V.     

Diphenylamino-fluorenylethylene derivatives for highly efficient blue organic light-emitting diodes

Highly efficient blue organic light-emitting diodes (OLEDs) were developed using diphenylamino-fluorenylethylene derivatives. In particular, OLEDs using compound 3 as a dopant in the emitting layer showed a maximum luminance of 12940 cd/m2 at 10 V; a luminous efficiency of 12.68 cd/A at 20 mA/cm2; a power efficiency of 5.24 Im/W at 20 mA/cm2, and CIE(x,y) coordinates of 0.181, 0.295 at 10 V. Furthermore, a deep blue OLED using dopant 2 with CIE coordinates of (0.154, 0.129) exhibited a maximum luminance of 5315 cd/m2 at 10 V; a luminous efficiency of 4.11 cd/A at 20 mA/cm2, and a power efficiency of 1.66 Im/W at 20 mA/cm2.     

Highly efficient blue light-emitting materials based on arylamine substituted DPVBi derivatives

A series of arylamine substituted DPVBi derivatives (1-4) were synthesized via the Horner-Wadsworth-Emmons reaction. Their electroluminescent properties were examined by fabricating a multilayer OLED device with the following structure: ITO/DNTPD (40 nm)/NPB (20 nm)/2% DPVBi derivatives (1-4) doped in MADN (20 nm)/Alq3 (40 nm)/Liq (1.0 nm)/Al. All devices showed efficient blue emission. In particular, a high efficiency blue OLED was fabricated using compound 1 as a dopant in the emitting layer. The maximum luminance, luminous efficiency, power efficiency and CIE coordinates of the blue OLED using compound 1 as a dopant were 16110 cd/m2 at 10 V, 10.1 cd/A at 20 mA/cm2, 4.37 Im/W at 20 mA/cm2, and (x = 0.197, y = 0.358) at 8 V, respectively. Moreover, a device using compound 4 as the dopant exhibited efficient deep blue emission with a luminance, luminous efficiency, power efficiency and CIE coordinates of 7005 cd/m2 at 10 V, 6.25 cd/A at 20 mA/cm2, 2.50 Im/W at 20 mA/cm2 and (x = 0.151, y = 0.143) at 8 V, respectively.     

Red-phosphorescent OLEDs employing iridium (III) complexes based on 5-benzoyl-2-phenylpyridine derivatives

A series of red-phosphorescent iridium (III) complexes 1-4 based on 5-benzoyl-2-phenylpyridine derivatives was synthesized. Their photophysical and electrophosphorescent properties were investigated. Multilayered OLEDs were fabricated with a device structure ITO/4,4′,4″-tris(N-(naphtalen-2-yl)-N-phenyl-amino)triphenylamine (60 nm)/4,4′-bis(N-naphtylphenylamino)biphenyl (20 nm)/Ir(III) complexes (8%) doped in 4,4′-N,N′-dicarbazolebiphenyl (30 nm)/2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (10 nm)/tris(8-hydroxyquinolinyl)aluminum(III) (20 nm)/Liq (2 nm)/Al (100 nm). All devices exhibited efficient red emissions. Among those, in a device containing iridium complex 1 dopant, the maximum luminance was 14200 cd/m² at 14.0 V. Also, its luminous, power, and quantum efficiency were 10.40 cd/A, 3.44 lm/W and 9.21% at 20 mA/cm², respectively. The peak wavelength of the electroluminescence was 607 nm, with CIE coordinates of (0.615, 0.383) at 12.0 V, and the device also showed a stable color chromaticity with various voltages.     

Single dopant white electrophosphorescent light emitting diodes using heteroleptic tris-cyclometalated Iridium(III) complexes

We report single dopant single emissive layer white organic electroluminescent (EL) device based on the heteroleptic tris-cyclometalated iridium(III) complex, Ir(dfppy)₂(pq), as the guest, where dfppy and pq are 2-(2,4-difluorophenyl) pyridine and 2-phenylquinoline, respectively, and 1,4-phenylenesis(triphenylsilane) (UGH2) as the host. The maximum luminous and power efficiencies of the device were 11.00 cd/A (J = 0.05 mA/cm²) and 5.60 lm/W (J = 0.001 mA/cm²), respectively. The CIE coordinates of the device with Ir(dfppy)₂(pq) are (0.443, 0.473) and the EL spectrum of device shows emission band at 473 and 544 nm, at the applied voltage of 12 V. The similar phosphorescent decay rate of two ligands can lead to emit luminescence in two ligands at the same time.     

A new yellow fluorescent dopant for high-efficiency organic light-emitting devices

We describe the design and synthesis of a sterically hindered yellow dopant, tetra(t-butyl)rubrene (TBRb) which, when doped in either 1,4-bis[N-(1-naphthyl)-N′-phenylamino]-biphenyl or aluminum tris(8-hydroxyquinoline) (Alq₃) as emitter, shows nearly 25% increase in luminance efficiency over that of the state-of-the-art rubrene (Rb) device without significantly effecting its corresponding color. At 5% doping in Alq₃ and 20 mA/cm² current drive condition, the electroluminescence efficiency of TBRb reaches 8.5 cd/A and 2.8 lm/W with a yellow color of Commission Internationale de l'Eclairage chromaticity coordinates (CIE_x,y) = [0.52, 0.48], which is among the best ever reported for yellow electrofluorescence in organic light-emitting devices.     

Blue electroluminescent materials based on 2,7-distyrylfluorene for organic light-emitting diodes

A series of blue fluorescent 9,9-diethyl-2,7-distyryl-9H-fluorene derivatives with various capping moieties such as diphenylamino; diphenylphosphino; triphenylsilyl; phenoxy; phenylmercapto; phenylselenoxy; and triphenymethyl groups were synthesized using the Honor-Emmons reaction. The highest occupied molecular orbital-lowest unoccupied molecular orbital energy levels were characterized with a photoelectron spectrometer and rationalized with quantum mechanical density functional theory calculations. The electroluminescent properties were explored through the fabrication of multilayer devices with a structure of Indium-tin-oxide/N,N′-diphenyl-N,N′-(1-napthyl)-(1,1′-phenyl)-4,4′-diamine/2-methyl-9,10-di(2-naphthyl)anthracene:blue dopants (5-15 wt.%)/4,7-diphenyl-1,10-phenanthroline/lithium quinolate/Al. All devices, except that using NPh₂, exhibited a Commission Internationale de I'Eclairage (CIE) y value less than 0.19. The best luminous efficiency of 3.87 cd/A and external quantum efficiency of 2.65% at 20 mA/cm² were obtained in a device comprising the 4-phenylsulfanyl capped 9,9-diethyl-2,7-distyrylfluorene derivative with CIE coordinates (0.16, 0.18).     

Improving light efficiency of white polymer light emitting diodes by introducing the TPBi exciton protection layer

We fabricated and evaluated the efficient white polymer light emitting diode (WPLED) by introducing TPBi exciton protection layer with ITO/PEDOT:PSS/PFO:MEH-PPV/TPBi/LiF/Al structure. PFO and MEH-PPV were prepared by the spin coating as the light emitting host and guest materials. TPBi was used as exciton protection material. The dependences of the MEH-PPV concentrations into the PFO (PFO:MEH-PPV) on the optical and electrical properties of the WPLEDs were investigated. The effect of the introduction of TPBi layer was studied by means of the property comparison between the samples with and without TPBi layer. The maximum luminance with 1480 cd/m² was obtained at the MEH-PPV concentration of 1.0 wt.% for the ITO/PEDOT:PSS/PFO:MEH-PPV/LiF/Al structure. In addition, the maximum luminance and current efficiency of the WPLED with TPBi layer were 7560 cd/m² at 12 V and 7.8 cd/A at 10 cd/m², respectively. The CIE color coordinates for WPLED with 1.0 wt.% MEH-PPV concentration was found to be (x, y) = (0.36, 0.33), showing pure white color.     

Orange-red phosphorescent OLEDs using iridium(III) complexes with benzoylphenylpyridine ligands containing fluorine and trifluoromethyl groups

We have designed and synthesized four orange-red phosphorescent Ir(III) complexes based on the benzoylphenylpyridine ligand with fluorine and trifluoromethyl substitution. Multilayered OLEDs were fabricated using these complexes as dopant materials. Particularly, by using 1 as a dopant in the emitting layer, a highly efficient orange-red OLED was fabricated, showing a maximum luminance of 10410 cd/m2 at 10 V, a luminous efficiency of 17.47 cd/A, a power efficiency of 7.19 Im/W, an external quantum efficiency of 6.27% at 20 mA/cm2, respectively, and CIE(x,y) coordinates of (0.51, 0.48) at 10 V. Furthermore, a red OLED using dopant 2, with CIE(x,y) coordinates of (0.61, 0.39), exhibited a maximum luminance of 5797 cd/m2 at 10 V, a luminous efficiency of 11.43 cd/A at, a power efficiency of 4.12 Im/W, and an external quantum efficiency of 6.62% at 20 mA/cm2, respectively.     

Tunable red emission by incorporation of a rubrene derivative in p-type and n-type hosts in organic light emitting devices

A red-emitting rubrene derivative, 2-formyl-5,6,11,12-tetraphenylnaphthacene (2FRb) was separately doped into 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) and tris-(8-hydroxyquinoline) aluminum (Alq₃) as the emitting layer. The emission can be tuned from 580 nm to 607 nm in NPB host and 560 nm to 622 nm in Alq₃ host. The Alq₃-hosted devices show better performances: more saturated pure red emission peaking at 622 nm with CIE_x,y = [x = 0.65, y = 0.35], a maximum luminance efficiency of 2.42 cd/A and a maximum luminance of 3100 cd/m² by doping 3.2 wt.% 2FRb in Alq₃ host. It indicates that the derivative of rubrene is a promising bipolar dopant for red light-emitting device.     

Efficient fluorescence from 9,10-bis(m-tolylphenylamino)anthracene doped into a blue matrix in Si-based top-emitting organic light-emitting diode

We demonstrate an efficient Si-based top-emitting organic light-emitting diode using a fluorescent emitting system composed of a green dye of 9,10-bis(m-tolylphenylamino)anthracene (TPA) doped into a blue matrix of 9,9′,10,10′-tetraphenyl-2,2′-bianthracene (TPBA). The device shows green emission with a maximum luminous efficiency of 3.3 cd/A and a power efficiency of 2.3 lm/W. The maximum luminance reaches 1.3 × 10⁴ cd/m² at a driving voltage of 12 V. The excellent performances partially resulted from effective energy transfer in the emitting system of [TPBA: 2 wt.% TPA]. In addition, the emission spectra exhibit negligible variation with increasing viewing angles, indicating a weak microcavity effect because of low reflectance of Si anode.     

Highly efficient blue light-emitting diodes based on diarylanthracene/triphenylsilane compounds

New host materials have been designed and synthesized, (4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)triphenylsilane (ANPTPS) and (9,9-dimethyl-7-(10-(naphthalen-2-yl)anthracen-9-yl)-9H-fluoren-2-yl)triphenylsilane (ANFTPS), and photophysical characteristics investigated to determine suitability as candidates for blue light-emitting materials. To explore the electroluminescent properties, multilayered OLEDs were fabricated with the device structure of ITO/NPB/Host (ANPTPS and ANFTPS): 8% Dopant (PFVtPh and PCVtPh)/Bphen/Liq/Al. By using a host (ANPTPS) and a dopant (PFVtPh) as the emitting layer, high-efficiency blue OLEDs were fabricated with a maximum luminance of 3991 cd/cm2 at 8.0 V, a luminous efficiency of 5.99 cd/A at 20 mA/cm2, a power efficiency of 3.11 lm/W at 20 mA/cm2, an external quantum efficiency of 4.13% at 20 mA/cm2, and CIEx, y coordinates of (x = 0.15, y = 0.18) at 8.0 V.     

High-efficiency white organic light-emitting devices with a non-doped yellow phosphorescent emissive layer

Highly efficient phosphorescent white organic light-emitting devices (PHWOLEDs) with a simple structure of ITO/TAPC (40 nm)/mCP:FIrpic (20 nm, x wt.%)/bis[2-(4-tertbutylphenyl)benzothiazolato-N,C²′] iridium (acetylacetonate) (tbt)₂Ir(acac) (y nm)/Bphen (30 nm)/Mg:Ag (200 nm) have been developed, by inserting a thin layer of non-doped yellow phosphorescent (tbt)₂Ir(acac) between doped blue emitting layer (EML) and electron transporting layer. By changing the doping concentration of the blue EML and the thickness of the non-doped yellow EML, a PHWOLED comprised of higher blue doping concentration and thinner yellow EML achieves a high current efficiency of 31.7 cd/A and Commission Internationale de l'Eclairage coordinates of (0.33, 0.41) at a luminance of 3000 cd/m² could be observed.     

5-Isobutyryl-2-phenylpyridine-derived iridium complexes for red phosphorescent light-emitting diodes

For the development of efficient red materials in organic light emitting diodes, a series of cyclometalated iridium complexes with 5-isobutyryl-2-arylpyridine-derived ligands were synthesized. Complexes 1-4 exhibited red phosphorescence with quantum yields of 0.16-0.48 in degassed CH2Cl2. An OLED device employing iridium complex 3 as a dopant exhibited the best performance with a maximum luminance of 35500 cd/m2 at 14 V and luminance and power efficiencies of 15.5 cd/A and 6.23 Im/W at 20 mA/cm2, respectively. In the device employing complex 2 as the dopant, the maximum luminance was 6300 cd/m2 at 14 V and the maximum luminance efficiency and power efficiencies were 5.23 cd/A and 3.16 Im/W at 5.2 V, respectively, with CIE coordinates of (0.66, 0.32) at 9.0 V, close to the saturated red emission.     

All fluorescent and high color rendering index white organic light-emitting devices with improved color stability at high brightness

We have demonstrated high color rendering index (CRI) white organic light-emitting devices using a multilayer structure based on all fluorescent emitters. The CRI of white light can be easily tuned by adjusting the thickness of the blue emitting layer (B-EML). In particular, the device with 8-nm-thick B-EML obtains very high CRI values (91-92) over a wide range of luminance (4000-23,000 cd/m²). Furthermore, the Commission Internationale De L'Eclairage coordinates of the device is rather stable and the variation is only (± 0.005, ± 0.003) over 4000-23,000 cd/m². The values are very close to white light equivalent energy point of (0.333, 0.333). We attribute these unique performances to the competition of the two mechanisms of the carrier trapping of the red dopant and efficient förster energy transfer in the blue emitting layer.     

Modified DCM-type materials for red fluorescent organic light-emitting diodes

A series of red emitters 1-3 based on modified DCM were synthesized and their electroluminescent properties were investigated. A device employing red emitter 2 as a dopant exhibited efficient red emission with maximum luminous efficiency of 1.87 cd/A, maximum power efficiency of 0.78 lm/W, maximum external quantum efficiency of 1.52%, and CIE coordinates of (0.65, 0.35) at 7.0 V.