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 similar to 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. (c) 2005 Elsevier B.V. All rights reserved.