Carbazole-based hole-transporting materials for electroluminescent devices

Two kinds of carbazole-based molecules connected with diphenylamine and carbazole are synthesized by modified Ullmann reaction. Comparative study on their thermal stability, redox behavior, hole injection and transport properties are present. The results demonstrate that the carbazole-based molecules are very promising hole-transporting materials for electroluminescent devices.

Efficient red organic light-emitting devices based on a europium complex

An efficient organic light-emitting device using a trivalent europium (Eu) complex Eu(Tmphen)(TTA)(3) (TTA=thenoyltrifluoroacetone, Tmphen=3,4,7,8-tetramethyl-1,10-phenanthroline) as the dopant emitter was fabricated. The devices were a multilayer structure of indium tin oxide/N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1-biphenyl-4,4-diamine (40 nm)/ Eu complex:4,4-N,N-dicarbazole-biphenyl (1%, 30 nm)/2,9-dimethyl,4,7-diphenyl-1,10phenanthroline (20 nm)/AlQ (30 nm)/LiF (1 nm)/Al (100 nm). A pure red light with a peak of 612 nm and a half bandwidth of 3 nm, which is the characteristic emission of trivalent europium ion, was observed. The devices show the maximum luminance up to 800 cd/m(2), an external quantum efficiency of 4.3%, current efficiency of 4.7 cd/A, and power efficiency of 1.6 lm/W. At the brightness of 100 cd/m(2), the quantum efficiency reaches 2.2% (2.3 cd/A).

Blue organic light-emitting devices with an oxadiazole-containing emitting layer exhibiting excited state intramolecular proton transfer

We report a blue organic light-emitting device having an emissive layer of 2-(2-hydroxyphenyl)-5-phenyl-1,3,4-oxadiazole (HOXD), that exhibits excited state intramolecular proton transfer (ESIPT). The device had a luminance efficiency of 0.8 cd/A and a maximum brightness of 870 cd/m(2). Electroluminescence spectra revealed a dominating peak at 450 nm and two additional peaks at 480 and 515 nm with a full width at half maximum of 50 nm. Our studies indicate that some EL may originate from the triplet excitation state of the enol form of HOXD.

Synthesis and properties of alternating copolymers containing PPV and hole-transporting units for light-emitting devices

A series of alternating copolymers containing triphenylamine (TPA) moieties and oligomeric PPV segments in the main chain have been synthesized by Wittig condensation. The resulting polymers exhibit good thermal stability with decomposition temperatures (Tds) above 305 degreesC under nitrogen at 10 degreesC/min, and high glass transition temperatures (Tgs). They show intense photoluminescence in solution and film. The single-layer electroluminescent device using TAA-PV1 as emissive layer emits green light at 522nm with a turn-on voltage of 6V and maximum brightness of about 200cd/m(2) at 20V.

Effects of the morphologies and structures of light-emitting layers on the performance of organic electroluminescent devices

Organic electroluminescent devices with a structure of ITO/ploy (9-vinylcarbazole)/tris (8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag are fabricated at different substrate temperatures (77, 298, and 438 K) during Alq3 deposition. It is found that the surface morphologies of Alq3 thin films greatly affect the I-V characteristics of the devices by the contact area between metal cathode and light-emitting layer. There is an increase in the luminous efficiency of the devices in the order 77 K < 298 K < 438 K. We attribute this trend to different structures of Alq3 thin films. (C) 2001 American Institute of Physics.

Bright green organic electroluminescent devices based on a novel thermally stable terbium complex

A navel thermally stable terbium carboxylate complex, Tb(MTP)(3)(phen) (MTP=monotetradecyl phthalate, phen=1,10-phehanthroline), was synthesized and characterized. The device structure of glass substrate/indium-tin-oxide/poly(p-phenylenevinylene) (PPV)/poly (N-vinycarbazole) (PVK):Tb(MTP)(3)(phen): 1,3,4-oxadizole derivative (PBD)/tris(8-hydroxyquinoline) (Alq(3))/aluminum (Al) was employed to study the electroluminescent properties of Tb(MTP)(3)(phen). A green emission with extremely sharp spectral band of less than 10 nm at 544 nm peak wavelength was observed. A maximum luminance of 152 cd/m(2) and an external quantum efficiency of 0.017% were achieved at a drive voltage of 24 V. A possible mechanism of energy transfer based on the polymer doped with lanthanide organic complex was also proposed.

Bright red organic electroluminescent devices based on a soluble rare earth complex Eu(TTA)(3) Phen

An Electroluminescent device with PVK film doped with Eu(TTA)(3) Phen and PBD was fabricated. The device structure of glass substrate/indium-tin-oxide/PPV/PVK : Eu(TTA)3 Phen : PBD/Alq(3)/Al was employed. A sharply red electroluminescence with a maximum luminance of 56. 8 cd/m(2) at 48 V was achieved.

Electroluminescent devices based on monohexadecyl phthalate terbium

Electroluminescent devices with PVK film doped with monohexadecyl phthalate terbium and PBD were fabricated. The device structure of glass substrate/ITO/PPV/PVK:Tb(MHP)(3):PBD/Alq(3)/Al was employed. The emissive layer was formed by a spin-casting technique. The EL cells exhibited characteristic emission of terbium ions with a maximum luminance of 74 cd/m(2) at 18 V. (C) 1998 Elsevier Science S.A. All rights reserved.

Organic electroluminescent devices using rare earth complex Eu(DBM)(3) as an emitter

Eu3+ narrow band emitting EL device with PPV, Alq(3) as hole and electron transportation layers has been prepared. The emitting layer, which consists of PVK, Eu(DBM)(3) and PBD is formed by spin-casting method. A maximum luminance of 52cd.m(-2) is achieved from the device.

Bright red electroluminescent devices based on a soluble lanthanide complex Eu(DBM)(3)(phen)

Electroluminescent devices with PVK film doped with Eu(DBM)(3)(phen) and PBD were fabricated. The device structure of glass substrate/indium-tin-oxide/PPV/PVK:Eu(DBM)(3)-(phen):PBD/Alq(3)/Al was employed. The emissive layer was formed by spin-casting method. A sharply red electroluminescence with a maximum luminance of 114.4 cd/m(2) was achieved at 42 V.

Bright blue electroluminescent devices utilizing poly (N-vinylcarbazole) doped with fluorescent dye

Bright blue electroluminescent devices have been fabricated using poly (N-vinylcarbazole) (PVK) doped with perylene as the emissive layer, poly(p-phenylenevinylene) (PPV) as the hole-transporting layer, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), tris(8-hydroxyquinoline)aluminum (Alq(3)) as the electron-transporting layer, and Al as the cathode. A luminance of 700 cd/m(2) and a luminescent efficiency of 0.8% are achieved at a drive voltage of 36 V. In the experiment, it is found that the introduction of electron-transporting layer PBD has a great effect on the emissive color of the electroluminescent devices prepared by PVK doped with perylene. Yellow-green emission is observed from the device structure of glass substrate/indium-tin-oxide/PVK:perylene/Al. The possible emissive mechanisms are given. The effect of the transporting layer on the electroluminescence is also discussed. (C) 1997 Elsevier Science S.A.

Photoluminesence and electroluminescence of the blue emission of devices based on poly(p-phenylenevinylene) copolymers

Bright blue polymer light-emitting diodes have been fabricated by using the poly(p-phenylenevinylene)-based copolymers with 10 C long aliphatic chains as the electroluminescent layers, PBD in PMMA and Alq(3) as the electron-transporting layers, and aluminum as the cathode. The multilayer structure devices show 190 cd/m(2) light-emitting brightness at 460 nm, 15 V turn-on vol- tage. It is found that the intensities of photoluminescence and electroluminescence (EL) increase with increasing aliphatic chain length, the EL intensity and operation stability of these polymer light-emitting diodes can be improved by reasonable design of the structure.

手持通信设备的多通道文本输入研究

Recently，Handheld Communication Devices is developing very fast, extending in users and spreading in application fields, and has an promising future. This study investigated the acceptance of the multimodal text entry method and the behavioral characteristics when using it. Based on the general information process model of a bimodal system and the human factor studies about the multimodal map system, the present study mainly focused on the hand-speech bimodal text entry method. For acceptance, the study investigated the subjective perception of the accuracy of speech recognition by Wizard of Oz (WOz) experiment and a questionnaire. Results showed that there was a linear relationship between the speech recognition accuracy and the subjective accuracy. Furthermore, as the familiarity increasing, the difference between the acceptable accuracy and the subjective accuracy gradually decreased. In addition, the similarity of meaning between the outcome of speech recognition and the correct sentences was an important referential criterion. The second study investigated three aspects of the bimodal text entry method, including input, error recovery and modal shifts. The first experiment aimed to find the behavioral characteristics of user when doing error recovery task. Results indicated that participants preferred to correct the error by handwriting, which had no relationship with the input modality. The second experiment aimed to discover the behavioral characteristics of users when doing text entry in various types of text. Results showed that users preferred to speech input in both words and sentences conditions, which was highly consistent among individuals, while no significant difference was found between handwriting and speech input in the character condition. Participants used more direct strategy than jumping strategy to deal with mixed text, especially for the Chinese-English mixed type. The third experiment examined the cognitive load in the different modal shifts, results suggesting that there were significant differences between different shifts. Moreover, relevant little time was needed in the Shift from speech input to hand input. Based on the main findings, implications were discussed as follows: Firstly, when evaluating a speech recognition system, attention should be paid to the fact that the speech recognition accuracy was not equal to the subjective accuracy. Secondly, in order to make a speech input system more acceptable, a good method is to train and supply the feedback for the accuracy in training, which improving the familiarity and sensitivity to the system. Thirdly, both the universal and individual behavioral patterns were taken into consideration to improve the error recovery method. Fourthly, easing the study and the use of speech input, the operations of speech input should be simpler. Fifthly, more convenient text input method for non-Chinese text entry should be provided. Finally, the shifting time between hand input and speech input provides an important parameter for the design of automatic-evoked speech recognition system.