| Organic light emitting diodes (OLEDs) are attracting significant interest in present display and lighting due to the superior anvantages in wide viewing angle, fast response time, pastel colors, and flexible feasibility. In this paper, we primarily study on the fundamental investigation of conventional OLEDs including the electron injection mechanism, the novel structure of spacer layer and high efficient hybrid WOLED. These work, which shows great significance in improving internal carrier injection efficiency and the optimization of internal spacer layer structures, including the following parts:(1) R-4B and GIrl have been utilized as the phosphorescent dopant to the OLED. High efficient yellow OLED that are fabricated with a intermediate connectors having Bphen, shows a comparable EL efficiency. The device structure was ITO/MoO3 (40 nm)/NPB (40 nm)/TCTA (10 nm)/CBP:GIrl(14 vol%) (20 nm)/BPhen (x nm)/CBP:R-4B(6 vol%) (10 nm)/BCP (10 nm)/Alq3 (40 nm)/LiF (1 nm)/Al (1000 nm). The device emission color and luminescent properties can be adjusted by optimiting the thickness of Bphen. The maximum efficiency is 24.35 cd/A.The results prove that the space layer utilized in double emission layers WOLED can effectively control the carriers transmission and combination.(2) We investigated the effect of a transition layer between emitting layer on the performance of organic yellow electroluminescent device. The emitting layer structure was CBP:10 vol%R-4B/CBP:10 vol%GIrl 10 vol%R-4B/CBP: 10 vol%GIrl. The reference device shows the CBP:10 vol%R-4B/CBP:10 vol%GIrl as the emitting layer. To investigate the influence of different emitting layer structure in the yellow OLED device, two reference devices have been fabricated, which emitting layer structure were CBP:10 vol%Girl/CBP:10 vol% Gir1:10 vol%R-4B/CBP:10 vol%R-4B and CBP:10 vol%GIrl/CBP:10 vol%R-4B. The results proved that the transition layer can significantly improve the device luminance and current efficiency. The maximum brightness and maximum current efficiency can be reached 11120 cd/cm2 and 27.59 cd/A. Compare with the reference device, maximum brightness and maximum current efficiency have been increased by 265% and 56.18%, respectively. We attribute to this result to the follow reason, one reason was the transition layer eliminated the strict interface effects, reduced interface defects. The another reason was the transition layer increased the carrier mobility and the excitons combination rate, so as to enhanced the OLED performance.(3) We investigated the effect of transition layer on the performance of yellow OLED. Meanwhile, we also fabricated full phosphorescent WOLEDs, the device brightness is 7910 cd/m2 at 12 V. The current efficiency is 26.7 cd/A at 0.56 mA/cm2. The WOLED also shows stable color. When the voltage is 5 V,10 Vand 15 V, the device CIE coordinate shows (0.34,0.35), (0.33,0.36) and (0.31, 0.38), respectively. The designed WOLEDs owns a stable white light emission and high EL characteristics. By optimiting the doping ratio of FIrpic, the excellent energy transfer between the host emitter and guest emitter occurred. Due to this, the efficiency of carrier combination increased.(4) A novel interlayer composed by TCTA and TmPyPB has been successfully used to be a universal carrier switch. By dint of this interlayer, we developed high-performance hybrid WOLED. The two-color hybrid WOLED shows a maximum total CE and PE of 48.1 cd/A and 37.6 lm/W, respectively. While the three-color hybrid WOLED shows a maximum total CE and PE of 33.8 cd/A and 25.7 lm/W, respectively. And the color rendering index of the three-color hybrid WOLED are>75, which is already a sufficient level for many commercial lighting applications. In addition, both the two-color and three-color hybrid WOLED show low efficiency roll-off and stable color. Furthermore, devices with the new interlayer show much higher performance than devices with the most commonly used CBP and NPB interlayers. |
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