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  Physics Express 2013, 3: 19
  Research Article
 
Doping effect of phenanthroline diimide in the electron transport layer for red phosphorescent organic light-emitting devices
  Gwijeong Choa,b, Hyena Leea, Sungho Wood, Sungho Nama, Hwajeong Kima,c, Youngkyoo Kima  
     
a Organic Nanoelectronics Laboratory, Department of Chemical Engineering, Kyungpook National University, Daegu 702-701, Republic of Korea
b OLED Device Development Team, LG Display Co. Ltd., Paju-si, Gyeonggi-do 413-811, Republic of Korea
c Priority Research Center, Research Institute of Advanced Energy Technology, Kyungpook National University, Daegu 702-701, Republic of Korea
d Green Energy Research Division, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu 711-873, Republic of Korea

   
  Abstract  
  Here we report the effect of doping a phenanthroline diimide into an electron transport layer for red phosphorescent organic light-emitting devices (PHOLED). The phenanthroline diimide used as a dopant was bis-[1,10]phenanthrolin-5-yl-pyromellitic diimide (Bphen-PMDI) that has a wider band gap than the material (tris(8-hydroxyquinolinato)aluminum (Alq3)) used for the electron transport layer in the red PHOLEDs. The doping ratio of Bphen-PMDI to Alq3 was varied up to 2% by keeping the thickness of the electron transport layer. Results showed that small amount (0.2 ~ 0.5%) doping of Bphen-PMDI greatly enhanced the luminance (brightness) and reduced the driving voltage of red PHOLEDs though the device performance became worse by further increase of doping ratio. The improved performance at an optimum doping ratio has been attributed to the secondary electron injection role of the doped Bphen-PMDI molecules after taking electrons injected initially from the first electron injection layer (lithium fluoride).
     
  Keywords  
  Organic light-emitting devices; Electron transport layer; Phenanthroline diimide; Doping; Charge transport  
     
   
   
   
   
     

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