Efficiency improvement of organic light-emitting diodes depending on the thickness variation of BCP layer used for electron transport

In the devices structure of ITO/N, N´-diphenyl-N, N´bis(3-methylphenyl)-1, 1´-biphenyl-4, 4´-diamine (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 40 nm, 60 nm under a base pressure of 5 times 10^-6 Torr using at thermal evaporation, respectively. The TPD and Alq₃ layer were evaporated to be deposition rate of 2.5 Aring/s. And the BCP was evaporated to be at a deposition of 1.0 Aring/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.