Optimization of High-Performance Blue Organic

Optimization of High-Performance Blue Organic - Published...

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Optimization of High-Performance Blue Organic Light-Emitting Diodes Containing Tetraphenylsilane Molecular Glass Materials Li-Hsin Chan, ² Rong-Ho Lee, Chia-Fen Hsieh, Hsiu-Chih Yeh, ² and Chin-Ti Chen* Contribution from the Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, ROC, and Chutung, Hsinchu, Taiwan 310, ROC Received January 3, 2002 Abstract: Molecular glass material (4-(5-(4-(diphenylamino)phenyl)-2-oxadiazolyl)phenyl)triphenylsilane (Ph 3 Si(PhTPAOXD)) was used as the blue light-emitting material in the fabrication of high-performance organic light-emitting diodes (OLEDs). In the optimization of performance, five types of OLEDs were constructed from Ph 3 Si(PhTPAOXD): device I, ITO/NPB/Ph 3 Si(PhTPAOXD)/Alq 3 /Mg:Ag, where NPB and Alq 3 are 1,4-bis(1-naphylphenylamino)biphenyl and tris(8-hydroxyquinoline)aluminum, respectively; device II, ITO/NPB/Ph 3 Si(PhTPAOXD)/TPBI/Mg:Ag, where TPBI is 1,3,5-tris( N -phenylbenzimidazol-2-yl)benzene; device III, ITO/Ph 2 Si(Ph(NPA) 2 ) 2 /Ph 3 Si(PhTPAOXD)/TPBI/Mg:Ag, where Ph 2 Si(Ph(NPA) 2 ) 2 is bis(3,5-bis- (1-naphylphenylamino)phenyl)-diphenylsilane, a newly synthesized tetraphenylsilane-containing triarylamine as hole-transporting material; device IV, ITO/Ph 2 Si(Ph(NPA) 2 ) 2 /NPB/Ph 3 Si(PhTPAOXD)/TPBI/Mg:Ag; device V, ITO/CuPc/NPB /Ph 3 Si(PhTPAOXD)/Alq 3 /LiF/Al, where CuPc is Cu(II) phthalocyanine. Device perfor- mances, including blue color purity, electroluminescence (EL) intensity, current density, and efficiency, vary drastically by changing the device thickness (100 - 600 Å of the light-emitting layer) and materials for hole-transporting layer (NPB and/or Ph 2 Si(Ph(NPA) 2 ) 2 ) or electron-transporting material (Alq 3 or TPBI). One of the superior OLEDs is device IV, showing maximum EL near 19 000 cd/m 2 with relatively low current density of 674 mA/cm 2 (or near 3000 cd/m 2 at 100 mA/cm 2 ) and high external quantum efficiency of 2.4% (1.1 lm/W or 3.1 cd/A). The device possesses good blue color purity with EL emission maximum ( λ max EL ) at 460 nm, corresponding to (0.16, 0.18) of blue color chromaticity on CIE coordinates. In addition, the device is reasonably stable and sustains heating over 100 ° C with no loss of luminance on the basis of the annealing data for device V. Formation of the exciplex at the interface of NPB and Ph 3 Si(PhTPAOXD) layers is verified by EL and photoluminescence (PL) spectra studies on the devices with a combination of different charge transporting materials. The EL due to the exciplex ( λ max EL at 490 - 510 nm) can be properly avoided by using a 200 Å layer of Ph 3 Si(PhTPAOXD) in device I, which limits the charge-recombination zone away from the interface area. Introduction
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Optimization of High-Performance Blue Organic - Published...

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