Two dimeric trimeric phenylenvinylene derivative 2, 5, 2', 5'-tetrakis (4'-fluorostyryl) biphenyl (P-F-TSB) and 2, 5, 2', 5'-tetra (p-trifluoromethylstyryl)-biphenyl (TFM-TSB) have been synthesized as new electroluminescent (EL) materials. P-F-TSB exhibits good color purity, high luminance of blue light-emission in organic light-emitting devices. Maximum brightness and luminous efficiency are of 1828 cd/m2 and of 1.92 cd/A, respectively. CIE coordinates are x=0.20 and y=0.22. Interestingly, we can fabricate single layer white light-emitting device using TFM-TSB as emitting layer. The broad electroluminescence emission band may attribute to long-wavelength excimer and electromer emission in addition to the blue component from singlet excited state of individual TFM-TSB molecule. Furthermore, white-light emission can also be obtained with a typical three-layer structure of ITO/ NPB (50 nm)/ TFM-TSB (50 nm)/ Alq3 (30 nm)/LiF/Al device. The maximum brightness of this device is 809 cd/m2 at 217 mA/cm2 and 13V, and the maximum luminous efficiency is 1.49 cd/A at 11 mA/ cm2 and 8V.
Efficient white organic light-emitting devices are demonstrated by inserting a thin layer of tris (8-hydroxyquinoline) aluminum (Alq) doped with 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl) (DCJTB) into N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) layer. Alq without doping is used as an electron-transporting layer and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine or BCP) as an exciton-blocking layer. NPB layers are separated by the doped Alq layer, the layer that sandwiched between BCP and doped Alq layers acts as a blue-emitting layer, and the other as a hole-transporting layer. The doped Alq layer acts as a red and green-emitting as well as chromaticity-tuning layer, whose thickness and position as well as the concentration of DCJTB in Alq permit the tuning of the device spectrum to achieve a balanced white emission with Commission Internationale De L'Eclairage coordinates of (0.33, 0.33), which are largely insensitive to the applied voltages, especially at high brightness (>1000cd/m2). The device have maximum luminance and efficiency of 6745 cd/m2 and 2.56 cd/A, respectively.
Blue and white organic light-emitting devices using a novel dimeric trimeric phenylenvinylene (TPV) derivative , 2,5,2',5'-tetrakis(4'-biphenylenevinyl)-biphenyl (TBVB) containing a biphenyl center are fabricated. Structures of these devices are simple, where tris (8-hydroxyquinoline) aluminum (Alq) and N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) are used as electron-transporting and hole-transporting layers, respectively. In blue device, TBVB is used as light-emitting layer. The peak of electroluminescent (EL) spectra of the device with TBVB is at 468 nm, and its maximum efficiency is greatly higher than that of the reported oligomer poly(phenylenvinylene) (PPV) devices. By inserting an ultra thin layer of rubrene between TBVB and Alq layers, a fairy pure white OLED with CIE coordinates of (0.33, 0.34) is realized. Its maximum luminances and efficiencies are 4025 cd/m2 and 3.2 cd/A, respectively.
We studied electron injection form Al cathode into the tris(8-hydroxyquinoline)aluminum (Alq3). When a thin CsCl layer is inserted between Alq3 and Al, a substantial enhancement in electron injection is observed. The results show that the device with the cathode containing the ultrathin CsCl layer has a higher brightness and electroluminescent efficiency than the device without this layer. Further, organic light-emitting devices (OLEDs) based on tris-(8-hydroxyquinoline)aluminum using a trilayer of CsCl/LiF/Al as cathodes have been fabricated. The results show that the device with the cathode containing 0.5 nm CsCl layer and 1.0 nm LiF layer has a higher brightness and electroluminescent efficiency than that of the device with LiF/Al or CsCl/Al cathodes. The maximum EL efficiency of the CsCl/LiF/Al cathode device is 3.41 cd/A, which is higher than the 2.74 cd/A of the LiF/Al device and 2.49 cd/A of the CsCl/Al device.
A novel blue organic light emitting diode is fabricated based on a new organic material. Dipyrrole3, which can emit a pure blue light. The Dipyrrole3 is used as a dopant and is doped into an electron-transporting hose. NPB is used as the hole transport layer. The device consists structure or ITO/NPB/Begg2:Dipyrrole3 (100:5)/BePP2/LiF/Al. It shows a bright blue light emission layer at 451nm and 480nm, the full width at half maximum is 61nm. The maximum luminescence is 2600cd/m2 at a voltage of 20V. The peak power efficiency is 0.7651m/W at a voltage of 7V.
A white light-emitting organic/polymeric electroluminescent (EL) device with multilayer thin-film structure is demonstrated. The device structure of glass substrate/indium-tin oxide/poly(N- vinylcarbazole)/phenylpyridine beryllium(BePP2)/8- (quinolinolate)-aluminum (Alq) doped with 5,6,11,12- petraphenylnaphthacene/Alq/LiF/Al was employed. The turn-on voltage is as low as 2.9 V. Blue fluorescent BePP2 yellow fluorescent rubrene, and green fluorescent Alq are used as three primary colors. The Commission Internationale de l'Eclariage coordinates of the emitted light are at 10V, which is located in the white-light region. Bright white light, over 6800cd/m2, was successfully obtained at about 17V, and the maximum efficiency reaches to 1.38m/W at 8.5V.
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