| Appropriate device structures and material are help to improve the performance of organic light emitting diodes (OLEDs). The paper is mainly focused on a new periodic-multiple-emitting-layer (PMEL) structure and a new terbium complex. The important results in this paper are listed as following:1, OLEDs with periodic-multiple-emitting-layer structuresTwo series of OLEDs based on PMEL structures had been fabricated. One consists of alternating layer of Alq3 and PBD, the other consists of alternating layer of NPB and BCP. The highest brightness and efficiency of the green and blue devices with two periodic multiple emitting layers were 10.5 and 4.4 times, 2.75 and 1.45 times than that of conventional green and blue devices without the PMEL structures, respectively. The improvement in the performance of devices was attributed to the improved electrons and holes balance in the emitting layers. At the same time, the number of periodic layers influences the performance of devices.2, A new terbium complexA new rare earth complex TbGd(BA)6(bipy)2 was doped into poly N-vinylcarbazole (PVK). The luminescent characteristics of the blend film of PVK and TbGd(BA)6(bipy)2 with different mass ratios were studied. The photoluminescence of terbium complex rooted in both exterior excitated directly and energy transferred from PVK to terbium complex. However, there were two means to produce the electroluminescence of terbium complex: one was by energy transfer from PVK to terbium complex; the other was by direct charge trapping on terbium complex. In multi-layer devices, carrier composite region was restricted at the interface of emitting layer and holes blocking layer due to high HOMO level of BCP. Enhancing electric field, emission from terbium complex was getting saturation gradually and weak emission from PVK was observed. From the optimized multi-layer device, green emission from terbium complex had been obtained with the highest EL brightness of the device of 213cd/m2.
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