Stock material or miscellaneous articles – Composite – Of inorganic material
Patent
1996-02-07
1998-08-11
Nold, Charles
Stock material or miscellaneous articles
Composite
Of inorganic material
428917, 313504, 548125, H05B 3314
Patent
active
057925674
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to novel triazole derivatives and organic electroluminescent devices produced therefrom.
BACKGROUND ART
It has been considered that light emission of an organic electroluminescent device is caused by the phenomenon where holes and electrons injected from electrode are recombined within a luminescent layer to generate excitons, and the excitons excite molecules of luminescent materials constituting the luminescent layer. By employing fluorescent dye as a luminescent material, there can be obtained an emission spectrum as an electroluminescence, being equivalent to photoluminescence of the dye molecules.
Tang and Vanslyke recently proposed a device comprising two layers of a hole-transport layer and an electron-transport luminescent layer which efficiently emits green light at a lower voltage (about 10 V) compared with conventional organic electroluminescent devices having single-layer 913!. The structure of the device is composed of an anode, a hole-transport layer, an electron-transport luminescent layer and a cathode, all of which are formed in this order on a glass substrate.
In this device, the hole-transport layer not only allows holes to be injected from the anode into the electron-transport luminescent layer, but prevents electrons injected from the cathode from escaping into the anode without recombining with the holes, so that the electrons are enclosed in the electron-transport luminescent layer. Thus, the electron confinement effect due to the hole-transport layer facilitates the recombination of the holes and the electrons compared with the conventional single-layer structure devices, resulting in substantial decrease in drive voltage.
Saito et al. showed that not only electron-transport layers but hole-transport layers can be the luminescent layer in the two-layer 55 (1989) 1489!.
Saito et al. also proposed a three-layer structure organic electroluminescent device wherein an organic luminescent layer is interposed between a hole-transport layer and an electron-transport layer (1988) L269!.
The two-layer structure device of Saito et al. is composed of an anode, a hole-transport luminescent layer, an electron-transport layer and a cathode, all of which are formed in this order on a glass substrate. In contrast to the previous device, the electron-transport layer not only allow electrons to be injected from the cathode into the hole-transport luminescent layer, but prevents the holes injected from the anode from escaping into the cathode while avoiding the recombination with the electrons, so that the holes are enclosed in the hole-transport luminescent layer. This hole confinement effect due to the electron-transport layer realizes substantial decrease in drive voltage, as in the previous device.
The three-layer structure device of Saito et al. was attained by a further improvement in the device of Tang et al. This device is composed of an anode, a hole-transport layer, a luminescent layer, an electron-transport layer and a cathode, all of which are formed in this order on a glass substrate. The hole-transport layer encloses electrons in the luminescent layer, and the electron-transport layer encloses holes in the luminescent layer, so that the recombination of the electrons and the holes within the luminescent layer is more efficient than the two-layer structure device.
Further, the electron-transport layer and the hole-transport layer prevent the excitons generated by the above recombination from escaping into either the anode or the cathode. Therefore, the three-layer structure device of Saito et al. may further increase the luminous efficiency.
Examples of hole-transport materials which constitute the above organic electroluminescent devices include aromatic tertiary amines such as triphenylamine. Examples of electron-transport material include oxadiazoles. Examples of luminescent material include tetraphenybutadiene derivatives, tris(8-quinolinolato)aluminum (III) complex, distyrylbenzene derivatives, distyrylbiphenyl derivatives and the like
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Applied Physics Letters, vol. 57, Aug. 6, 1990, pp. 531-533, Adachi et al.
Applied Physics Letters, vol. 63, No. 19, Nov. 8, 1993, Kido et al., pp. 2627-2629.
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Japanese J. Appl. Physical, vol. 32 (1993) pp. 917-920, Part 2, No. 7A, Jul. 1, 1993, Kido et al.
Department of Materials Science and Engineering, Yamagata University, Yonezawa, Ymagata 992, White Light-Emitting Organic El Devices Based on Poly(N-vinylcarbazole),pp. 1-8.
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Kido Junji
Kimura Hiroya
Okuda Nobuyuki
Okuda Yasuko
Osaka Hajime
Nold Charles
Sumitomo Electric Industries Ltd.
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