Efficiency Improvement of Organic Light-Emitting Diodes depending on the Thickness Variation of BCP Layer used for Electron Transport

Abstract

In the devices structure of ITO/N,N'- diph enyl-N,N'bis(3-methyphenyl)-1, 1'-biphenyl-4,4'-diam ine(TPD)/tris(8-hydroxyquinoline)aluminum (Alq3) electron-transport-layer(ETL) (2,9-Dimethyl-4,7-diphenyl-1, 10-phenanthroline(BCP))/Al, we have studied the efficiency improvement of organic light-emitting diodes depending on the thickness variation of BCP using electron transport layer. The thickness of TPD and Alq3 was manufactured 40nm, 60nm under a base pressure of 5x10(-6) Torr using at thermal evaporation, respectively. The TPD and Alq3 layer were evaporated to be deposition rate of 2.5 angstrom/s. And the BCP was evaporated to be at a deposition of 1.0 angstrom/s. As the experimental results, we found that the luminous efficiency and the external quantum efficiency of the device is superior to others when thickness of BCP is 5 nm. Also, operating voltage is lowest. Compared to the ones from the devices without BCP layer, the luminous efficiency and the external quantum efficiency were improved by a factor of four hundred ninety and five hundred, respectively. And operating voltage is reduced to about 2 V.