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An efficient blue organic light-emitting diode with 1,4-bis[2-(3-N-ethylcarbazoryl)vinyl]benzene doped into 4,4[sup ′]-N,N[sup ′]-dicarbazole-biphyenyl is reported. Maximum luminance and external quantum efficiency are 8500 cd/m[sup 2] and 2.6%. CIE-1931 coordinates are x=0.15, y=0.16. The device performance was further improved by introducing bis(2-methyl-8quinolinato)4-phenylphenolate aluminum to assist electron injection. The maximum luminance and quantum efficiency reached 11000 cd/m[sup 2] and 3.3%, respectively. Föster energy transfer and especially a carrier trapping mechanism are considered to dominate in the process of electroluminescence. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: In this letter, blue organic light-emitting diodes (OLEDs) with a different hole injection layer (MoO3 or m-MTDATA), and a different electron transport layer (Alq3 or BPhen) have been investigated. With 9,10-bis(2-naphthyl)-2-t-butylanthracene (TBADN) doped with (3wt.%) P-bis(P-N,N-diphenyl-aminostyryl)benzene (DSA-Ph) as an emitting layer, the typical device structure is ITO/HIL (5nm)/NPB (25nm)/EML (35nm)/ETL (15nm)/LiF (0.8nm)/Al (100nm). It has been found that MoO3//BPhen based device shows the lowest driving voltage and highest power efficiency among the referenced devices. At the current density of 20mA/cm2, its driving voltage and power efficiency is 5.2V and 4.2lm/W, which is independently reduced 48% and improved 44% compared with those of the m-MTDATA//Alq3 based one, respectively. The energy level diagram of the devices and single-carrier devices are studied to explain the reasons behind this improvement. The results strongly indicate that carrier injection ability and balance shows significant affects on the performance of OLED. [Copyright &y& Elsevier]

Abstract: Blue organic light-emitting devices based on wide bandgap host material, 2-(t-butyl)-9, 10-di-(2-naphthyl) anthracene (TBADN), blue fluorescent styrylamine dopant, p-bis(p-N,N-diphenyl-amino-styryl)benzene (DSA-Ph) have been realized by using molybdenum oxide (MoO3) as a buffer layer and 4,7-diphenyl-1,10-phenanthroline (BPhen) as the ETL. The typical device structure used was glass substrate/ITO/MoO3 (5nm)/NPB (30nm)/[TBADN: DSA-Ph (3wt%)](35nm)/BPhen (12nm)/LiF (0.8nm)/Al (100nm). It was found that the MoO3∥BPhen-based device shows the lowest driving voltage and highest power efficiency among the referenced devices. At the current density of 20mA/cm2, its driving voltage and power efficiency are 5.4V and 4.7Lm/W, respectively, which is independently reduced 46%, and improved 74% compared with those the m-MTDATA∥Alq3 is based on, respectively. The J–V curves of ‘hole-only’ devices reveal that a small hole injection barrier between MoO3∥NPB leads to a strong hole injection, resulting low driving voltage and high power efficiency. The results strongly indicate that carrier injection ability and balance shows a key significance in OLED performance. [Copyright &y& Elsevier]

Abstract: We demonstrate p–i–n organic light-emitting diodes (OLEDs) incorporating an n-doping transport layer which comprises 8-hydroxy-quinolinato lithium (Liq) doped into 4′7-diphyenyl-1,10-phenanthroline (Bphen) as ETL and a p-doping transport layer which includes tetrafluro-tetracyano-quinodimethane (F4-TCNQ) doped into 4,4′,4″-tris(3-methylphenylphenylamono) triphenylamine (m-MTDATA). In order to examine the improvement in the conductivity of transport layers, hole-only and electron-only devices are fabricated. The current and power efficiency of organic light-emitting diodes have been improved significantly after introducing a novel n-doping (Bphen: 33wt% Liq) layer as an electron transport layer (ETL) and a p-doping layer composed of m-MTDATA and F4-TCNQ as a hole transport layer (HTL). Compared with the control device (without doping), the current efficiency and power efficiency of Device C (most efficient) is enhanced by approximately 51% and 89%, respectively, while driving voltage is reduced by 29%. This improvement is attributed to the improved conductivity of the transport layers that leads to the efficient charge balance in the emission zone. [Copyright &y& Elsevier]

Abstract: White OLEDs with a different hole injection layer (MoO3 or m-MTDATA), and a different electron transport layer (Alq3 or Bphen) have been investigated. With 9,10-bis (2-naphthyl)-2-t-butylanthracene (TBADN) doped with 3% P-bis (P-N, N-diphenyl-aminostyryl) benzene (DSA-ph) and 0.05% 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7,-tetramethyl-julolidy-9-enyl)-4H-pyran (DCJTB) as white emitting layer, the MoO3/ /Bphen based device shows the lowest driving voltage and highest power efficiency among the referenced devices. At the current density of 20 mA/cm2, its driving voltage and power efficiency are 5.43 V and 4.54 lm/W respectively, which is independently reduced 40% and improved 57% compared with those of the m-MTDATA/ / Alq3 based one, respectively. The energy level diagram of the devices and single-carrier devices are studied to explain the reasons for the improvement. The results strongly indicate that carrier injection ability and balance shows a key significance in OLED performance. [Copyright &y& Elsevier]

Abstract: We demonstrated efficient red organic light-emitting diodes based on a wide band gap material 9,10-bis(2-naphthyl)anthracene (ADN) doped with 4-(dicyano-methylene)-2-t-butyle-6-(1,1,7,7-tetramethyl-julolidyl-9-enyl)-4H-pyran (DCJTB) as a red dopant and 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10(2-benzothiazolyl)quinolizine-[9,9a,1gh]coumarin (C545T) as an assistant dopant. The typical device structure was glass substrate/ITO/4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA)/N,N′-bis(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB)/[ADN:Alq3]:DCJTB:C545T/Alq3/LiF/Al. It was found that C545T dopant did not by itself emit but did assist the energy transfer from the host (ADN) to the red emitting dopant via cascade energy transfer mechanism. The OLEDs realized by this approach significantly improved the EL efficiency. We achieved a significant improvement regarding saturated red color when a polar co-host emitter (Alq3) was incorporated in the matrix of [ADN:Alq3]. Since ADN possesses a considerable high electron mobility of 3.1×10−4 cm2 V−1 s−1, co-host devices with high concentration of ADN (>70%) exhibited low driving voltage and high current efficiency as compared to the devices without ADN. We obtained a device with a current efficiency of 3.6cd/A, Commission International d’Eclairage coordinates of [0.618,0.373] and peak λ max =620nm at a current density of 20mA/cm2. This is a promising way of utilizing wide band gap material as the host to make red OLEDs, which will be useful in improving the electroluminescent performance of devices and simplifying the process of fabricating full color OLEDs. [Copyright &y& Elsevier]

Abstract: Organic light-emitting diodes with 8-hydroxy-quinolinato lithium doped 4′7-diphyenyl-1, 10-phenanthroline as electron transport layer (ETL), and etrafluro-tetracyano-quinodimethane doped 4,4′,4″-tris(3-methylphenylphenylamono) triphenylamine as hole transport layer (HTL) are demonstrated. The conductivity of carrier transport layers with different doping concentration is examined by hole-only and electron-only devices. Compared with the referenced device (without doping), the current efficiency and power efficiency of the p–i–n device are enhanced by approximately 51% and 89%, respectively. This improvement is attributed to the improved conductivity of the transport layers and the efficient charge balance in the emission zone. [Copyright &y& Elsevier]

A white organic light emitting diode (OLED) was fabricated in which a blue light emitting host DPVBi was doped with a red dye DCJTB. The device structure was ITO/CuPc/NPB/DPVBi:DCJTB/Alq/LiF/Al, where CuPc is copper phthalocyanine, NPB is N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine, DPVBi is 4,4′-bis(2,2-diphenylvinyl)-1,1′-biphenyl, DCJTB is 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran, and Alq is tris(8-quinolinolato) aluminium. White light emission was realized in an OLED with 0.08% DCJTB doping concentration by weight. The fabricated white OLED showed a little shift from blue to red with the increase of injection current, e.g. the CIE coordinates from (0.26, 0.32) at 4 mA/cm2 current density to (0.24, 0.30) at 400 mA/cm2 current density. The maximum luminance reaches 7822 cd/m2, and the maximum luminous efficiency is 1.75 lm/W (2.45 cd/A) at 20 mA/cm2. [Copyright &y& Elsevier]