A new device has been made by inserting thin LiF layer in N,N'-diphenyl-N,N'-bis(1-napthyl-phenyl)-1, 1'-biphenyl-4,4'-diamine (NPB), which has a configuration of ITO/NPB(20 nm)/LiF(0.5 nm)/NPB(20 nm)/ Alq(3)(60 nm)/LiF(0.5 nm)/Al. Compared with normal device, the device inserted LiF layer inside NPB (HTL) can improve its performance. The luminance and efficiency is about 1.4 and 1.3 folds high of the conventional structure, respectively. The suggestion mechanism is that the LiF in the NPB layer can block holes of NPB, and balance the holes and electrons. Consequently, there are more excitons formed to boost the diode's luminance and efficiency. And it may offer some valuable references for OLED's structure. (c) 2009 Published by Elsevier B.V.