High-Efficiency Nondoped Blue Organic Light-Emitting Devices with Reduced Efficiency Roll-Off

Nondoped Mile organic light-emitting devices with a structure of ITO/hole transporting layer (HTL)/2-diphenylamino-7-(2,2 ''-diphenylvinyl)-9,9'- spirobifluorene/electronic transporting layer (ETL)/LiF/Al are Fabricated. The performances of the devices are dependent oil the charge mobility, char-e injection, and energy level characteristics of HTL and ETL. The device with 4,4',4 ''-tris(3-methylphenylphenylamino)triphenylamine and 4,7-diphenyl-1,10- phenanthroline as HTL and ETL shows high efficiency mid brightness at low voltage (5.8 cd/A and 1000 cd/m(2) at 4.6 V). Furthermore, the device shows a slight efficiency roll-off We attributed this to the formation of 16% from the brightness at maximum current efficiency to 10 000 cd/m(2). We attributed this to the formation of it broader carrier recombination zone and relative charge-balancing in the device.