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10 April 2005 Blue organic light-emitting device with low driving voltage and high current efficiency
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In this paper, we report a high efficiency organic light-emitting device (OLED) with a high electron mobility electron transport layer (ETL) material and high efficiency blue dopant material. Typically, the mobility of a hole transport layer (HTL) material is much higher than that of an electron transport layer (ETL) material. Here we used the bis(10-hydroxyben-zo[h]quinolinato)beryllium (Bebq2) as the ETL material that exhibits superior electron mobility. It effectively reduced the driving voltage and increased the power efficiency. The blue dopant material was 4,4'-bis[2-(4- (N,N-diphenylamino)phenyl)vinyl]biphenyl (DPAVBi) in the 9,10-bis(2’-naphthyl) anthracene (BNA), that was the host material of the emitting layer (EML). At 100 cd/m2, the current efficiencies with different dopant concentration can be as high as 19.2 cd/A with the CIE coordinate at (0.154, 0.238). Driving voltage at 20mA/cm2 was 4.94 V of this device. With increasing the doping concentration, the drive voltage variation did not vary much and was within 0.6 V at 20 mA/cm2. The emitting mechanism in such a device may be mainly due to energy transfer rather than carrier trapping. CIE coordinate of such a device shifted toward blue with increasing current density due to intense light emission from the host material of the EML. The highest efficiency was achieved when doping concentration is 3%.
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Jiun-Haw Lee, Tien-Chun Lin, and Chi-Chih Liao "Blue organic light-emitting device with low driving voltage and high current efficiency", Proc. SPIE 5740, Projection Displays XI, (10 April 2005);

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