Zhiyuan Xie

White light emission induced by confinement in organic multiheterostructures

A technique for inducing white-light emission from organic multiheterostructures is proposed. The configuration of organic multiheterostructure white-light emitting diodes is ITO/TPD(50 nm)/BePP2(5 nm)/TPD(4 nm)/BePP2:rubrene(5 nm)/TPD(4 nm)/Alq3(10 nm)/Al. Triphenyldiamine derivative (TPD) is used as a hole-transporting layer and the potential barrier layers. Blue fluorescent phenylpyridine beryllium (BePP2), orange fluorescent rubrene, and green fluorescent aluminum complex (Alq3) are used as three primary colors. BePP2 and BePP2 doped with rubrene act as the potential wells sandwiched between TPD barrier layers, in which excitons are confined. Alq3 is used as an electron-transporting green-color emitter. The white-light emission spectrum covers a wide range of the visible region, and the Commission Internationale de l’Eclairage coordinates of the emitted light are (0.32, 0.38) at 9 V. The maximum brightness and luminous efficiency of this device are 4000 cd/m2 (at 17 V) and 0.4 lm/W, respectively.

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.

HIGH EFFICIENT GREEN EMISSION FROM ORGANIC MULTI-QUANTUM WELLS STRUCTURE

Organic green light emitting devices (LEDs) with multi-quantum wells (MQWs) structure were fabricated. Aromatic diamine was used as hole-transporting layer and potential barrier layer; tris (8-hydroxyquinoline) aluminum acted as electron transporting layer and MQWs green emitting layer. The influence of the barrier layer thickness and quantum well number to the device performance was also investigated. The barrier thickness must be thin (such as 4 nm) enough to tunnel through and distribute charge carriers uniformly in different wells (mainly electrons). The organic MQWs LEDs showed enhanced electroluminescent efficiencies. Maximum luminous efficiency and external quantum efficiency were 1.24 lm/W and 1.04%, respectively.

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.

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.

ENHANCED HOLE INJECTION AND BRIGHTNESS OF ORGANIC ELECTROLUMINESCENT DEVICES WITH INDIUM TIN OXIDE SURFACE MODIFICATION USING OXYGEN PLASMA TREATMENT

The improvement of indium tin oxide (ITO) anode contact to organic electroluminescent devices via oxygen plama treatment is investigated. Enhanced hole-injection efficiency improved the performance of organic light-emitting devices. The injection current increased by 1-2 orders of magnitude and the turn-on voltages droped several volts. Much higher injection current could be applied to achieve much higher brightness. Maximum brightness and luminous efficiency can reach to about 4000 cd/m2 and 0.3lm/W for the structure of ITO/TPD/Alq3/Al, respectively.

Organic single-quantum-well electroluminescent device

A new kind of single-quantum-well electroluminescent (EL) device consists of a hole transport N,N-Bis(3-methyphenyl)-N,N-diphenylbenzidine(TPD) layer, and electron transport 8-(quinolinolate)-aluminum(Alq) layer and a light emitting layer of Alq doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) has been fabricated by the multisource-type high-vaccum organic molecular deposition. The dopant rubrene is as a potential well, and the undoped Alq layer is as a barrier layer. The EL spectra shows the spectral narrowing and the emission peak energy blue-shift, and the efficiency and luminance of the device have been significantly improved. The experimental phenomena is explained as the result of recombination of carriers from the quantized energy state.

Organic electroluminescent devices and their application

Several organic electroluminescent devices have been fabricated by multi-source high vacuum deposition system. For high brightness organic electroluminescent device, the maximum brightness is over 40000 cd/m2. For quantum well structures, quantum size effect has been investigated and the high light emission efficiencies of the devices have been obtained. White-light emission from organic multi-quantum well structures is proposed at first. Brightness of the white-light MQW devices reaches 4000 cd/m2 at 17 V.