Study On The Fabrication And Performance Of OLEDs With Low Driving Voltage And High Efficiency

With the rapid development of information technology, the high- performance display devices are widely applied in various fields. The organic light-emitting diodes(OLEDs) have drawn much attention due to their numerous advantages, such as low power consumption, high brightness, wide viewing angles, surface light-emitting, full-color display, flexibility and so on. For the commercial applications in the future, the OLED requires low driving voltage, and needs to be improved in efficiency simultaneously. Therefore, a series of OLEDs have been fabricated to explore the realization of device’s low driving voltage and high efficiency in this work. The specific contents are listed as follows:1. The OLEDs have been fabricated by using F4-TCNQ doped Mo O3 as hole buffer layer. We analyzed the influence on the device’s performance by introducing of hole buffer layer with different doping concentration and thickness. From the energy levels of the optimized device, it can be found that the hole injection barrier has been reduced and the surface morphology of the organic layers would be smooth after inserting the buffer layer, which resulted in the better injection and transport of the holes. When the thickness and doping concentration of the doped hole buffer layer are 2 nm and 50%, respectively, the OLED presents an efficient luminance. The turn-on voltage and driving voltage(at 1000 cd/m2) is 2.8 V and 5.5 V, which has been reduced 1 V and 2.3 V compared to those of the control device, respectively.2. Based on the high electron mobility, C60 was used as the electron transport layer(ETL). The organic materials Alq3, Bphen and TPBi were used as different electron buffer layer(EBL). A layered injection structure in OLEDs can be formed by combining the ETL with the EBL. By optimizing the thicknesses of ETL and different EBLs, the OLEDs with EBLs exhibited the improved EL performance compared to the device without EBL. The brightness and efficiency of the devices are obviously improved. Meanwhile the efficiency roll-off of these devices could be alleviated without compromise of current efficiency due to the balance of carrier injection and transport. Moreover, the EBLs also functioned as the protection layer for C60 layer.3. Combined the doped hole buffer layer F4-TCNQ:Mo O3 with layered electron injection and transport layers C60/Alq3 in one device unit, the low voltage driving OLED has been fulfilled. The turn-on voltage of 2.6 V and the driving voltage of 4.7 V(at 1000 cd/m2) have been achieved in optimum device, respectively. Compared with the traditional device, the turn-on voltage and driving voltage of optimum device are reduced by 31.6% and 35.9%, respectively. The current efficiency and the power efficiency of optimum device are increased by 94% and 164%, respectively. In addition, we fabricated the OLEDs with a p-type EML material TC-1759 to verify the universality of the similar PIN structure. The results also showed that the blue OLEDs with this structure have presented a high efficiency under a relatively low driving voltage.