Improving the efficiency of organic light emitting devices by using co-host electron transport layer

By engineering a new cohosting system of tris(8-hydroxyquinoline) and 4,7-diphenyl-1,10-phenanthroline in the electron transport layer, the current efficiency of the organic light emitting diode is improved by 34% to 4.3 cd/A as compared to the device with a single host of Alq 3 as the electron transport layer. The maximum luminance is over 16,000 cd/m 2 at the bias of 22 V and the current of 475 mA/cm 2, which is ∼ 73% higher than the single host Alq 3 device without optimizing the layer thickness. The reasons for the improvement will be investigated. The results strongly indicate that the knowledge of bulk conductivity engineering of organic n-type transporters shows practical significance in OLED applications.