Kaixia Yang

High-brightness organic double-quantum-well electroluminescent devices

An organic double-quantum-well structure electroluminescent device fabricated by a doping method is demonstrated. The device consists of N,N′-bis-(1-naphthl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) used as a hole transporter, undoped tris(8-quinolinolato) aluminum (Alq) as a barrier potential or electron transporter, and Alq doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) as a potential well and emitter, and has the following structure: indium tin oxide/NPB/Alq:rubrene/Alq/Alq:rubrene/Alq/Mg/Al. The maximum brightness and efficiency reach 48 000 cd/m2 and 4.59 lm/W, respectively. The present double-quantum-well structure device shows higher brightness and higher efficiency than those of the common heterostructure devices.

EFFECT OF WELL NUMBER ON ORGANIC MULTIPLE-QUANTUM-WELL ELECTROLUMINESCENT DEVICE CHARACTERISTICS

A doping technique for fabricating organic multiple-quantum-well electroluminescent (EL) devices is demonstrated. This device consists of N,N′-Bis(3-methyphenyl)-N,N′-diphenylbenzidine used as a hole transporter, undoped tris(8-quinolinolato) aluminum (Alq) as a barrier potential or electron transporter, and Alq doped with 5,6,11,12-tetraphenylnaphthacene as a potential well and an emitter. Our experimental results suggest that the double-quantum-well EL devices show the optimum emission characteristics. The efficiency and the luminance of the device achieve 15.7 lm/W and 7500 cd/m2, respectively.

Organic low-dimensional structure electroluminescent material characteristics and devices

Photoluminescence (PL) characteristics of organic doped films are studied as a function of dopant concentration, doped layer thickness. The luminescence properties of doped films are decided by Förster energy transfer rate between host and guest and fluorescence quenching effect of guest. For Alq:rubrene doped film at 5% doping level, we fabricated and characterized organic doped quantum-well structure device, and observed significant quantum size effect. For Alq:QAD doping system, at low doping level of 0.4%, the intermolecular spacing between QAD molecules is relatively large, the interaction between neighboring QAD molecules is very small due to the strong localization of the carriers in the single QAD molecules, the PL properties of Alq:QAD doped films only depends on the PL properties of single isolated QAD molecules, which is somewhat similar to the inorganic quantum dot structure. We also reported the electroluminescent performance of the Alq:QAD system.

Effects of alternate doped structures on organic electroluminescent devices

Abstract Two organic electroluminescent (EL) devices with alternate doped structures have been fabricated under high vacuum deposition system. One of the structures consists of alternating layers of doped tris(8-quinolinolato) aluminum (Alq) and undoped Alq. The other consists of alternating layers of doped N , N ′-bis-(1-naphthyl)- N , N ′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and undoped NPB. Effects of the designed structures on blue-shift of the emission peak energy and on the brightness and efficiency of the organic EL devices are observed. Uniquely, the efficiency of the device with the latter structure is relatively independent on the drive voltage in a wide range from 5 to 13V.

Effect of rubrene on characteristic of red organic electroluminescent device doped with rubrene

Abstract Red organic electroluminescent device based on Alq3 doped with DCM and rubrene is fabricated. N,N′-bis-(1-naphthl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) is used as the hole-transporting layer, tris(8-quinolinolato) aluminum (Alq3) doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) and 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) as the emitting layer, and undoped Alq3 as the electron-transporting layer. We examine the dominant transfer mechanism from rubrene to DCM by comparing between the PL and EL spectrum. When the doping concentration of rubrene (6%) is similar to that of DCM (4%), red emission is improved in terms of spectral purity in comparison with that of other doped devices.

Optical and electrical characteristics of organic electroluminescent devices with multiple-quantum-well structure

We report for the first time organic multiple-quantum-well-like electroluminescent (EL) devices fabricated by the doping technique. The EL device consists of N,N´-Bis(3-methyphenyl)-N,N´-diphenylbenzidine used as a hole transporter, undoped 8-(quinolinolate)-aluminium(Alq) as a barrier potential or an electron transporter, and Alq doped with 5,6,11,12-tetraphenylnaphthacene as a potential well and a light emitter. The effects of well width and well number on EL device properties are demonstrated. Compared with the characteristics of the heterojunction EL device, the single quantum well EL device shows higher efficiency and luminance, narrower spectrum and higher emission peak energy. Compared with the characteristics of quantum-well EL devices with different well number, our results indicated that the double-quantum-well EL devices have the optimum performance, the efficiency and the luminance of the device achieve 15.7 lm W-1 and 7500 cd m-2, respectively.

Improved performances of the organic light-emitting devices by doping in the mixed layer

The brightness, efficiency and lifetime of organic light-emitting diodes (OLEDs) were remarkably improved by doping in a mixed layer. In this device, the emitting layer consists of a mixture of α-naphthylphenybiphenyl amine (NPB), tris (8-hydroxyquinolinolate) aluminum (Alq3) (referred to as the mixed layer) and an emissive dopant 5,6,11,12-petraphenylnaphthacene (rubrene), where the concentration of NPB declined while the concentration of Alq3 was increased gradually in the deposition process. The device exhibited a maximum emission of 49,300 cd/m2 at a destroy voltage of 35 V and a maximum efficiency of 7.96 cd/A at 10 V, respectively. The efficiency improves twofold in comparison with the conventional doped devices. Meanwhile, the device exhibited superior operational stability with a half-life time of 1000 h at a starting luminance of 1000 cd/m2 by a constant current driver.

Graded doping in active layer for achievement of high brightness and efficiency organic light-emitting devices

A graded doping technique was presented to fabricate high brightness and high efficiency OLEDs, in which a copper phthalocyanine(CuPc) film acts as buffer layer (alpha) -naphthylphenybiphenyl amine(NPB) film as hole-transport layer and a tris(8-hydroxyquinolinolate)aluminum(Alq3) film as the electron-transport layer.The luminescent layer consists of the mixture of NPB,Alq3 and an emitting dopant 5,6,11,12-petraphenylnaphthacene(Rubrene), where the concentration of NPB raised while the concentration of Alq3 was declined gradually in the deposition process. The graded doping device exhibited the maximum emission of 50000cd/m2 at 35v and the maximum efficiency of about 8cd/A at 9v, respectively, which have been improved by four times in comparison with the conventional doped devices.

Highly efficient and bright doped organic electroluminescent diodes using an aluminum electrode

Remarkable improvement in efficiency and electroluminescence (EL) has been observed in an organic EL device, which consists of a hole-transport layer and a luminescent layer. The hole-transport layer is an N,N′-bis(3-methyphenyl)-N,N′-diphenylbenzidine film. The doped emitting layer consists of 8-(quinolinolate)-aluminum as the host and rubrene as the emission dopant. The doped cell with aluminum cathode demonstrated a luminance in excess of 20,000 cd/m2 and an external quantum efficiency of 2.7%, which is about four times and three times, respectively, greater than those of the undoped cell. The EL emission from the device shows spectral narrowing and a shift to higher energy.

Organic quantum well electroluminescent devices

For Alq:rubrene doped film at 7.4% doping level, we fabricated organic doped quantum-well structure device,and observed that maximum brightness and efficiency are 48000 cd/m2 and 4.59 1 m/w respectively. We have also researched MQW electroluminescent devices by using NPB:rebrene system, at doping level of 8%, maximum brightness reach 30000 Cd/cm2 and this MQW devices show a smoother efficiency as changing operation voltage.