Preparation And Research Of Low-Voltage High-Performance Red OLED

Organic light-emitting diodes are considered as the third generation of display technology because of their unique advantages in flat panel display and solid-state lighting.The driving voltage of OLED is closely related to the device's luminescence performances.In many lighting and display fields,OLED is required to have a low operating voltage.The low driving voltage can effectively reduce the unnecessary joule heat generated during the luminescence process,so as to ensure the stability of the devices.Therefore,reducing the driving voltage is one of the important technologies for the commercialization of OLED.In this thesis,red phosphorescent PQ2Ir(dpm)was used as the light-emitting material,m CP and Cz Si were used as host materials to prepare single-and dual-light-emitting layer OLED devices,and Tc Ta and bipolar BUPH1 were used as host materials to prepare singleand dual-light-emitting layer OLED devices.By optimizing the doping concentration of the light-emitting material and the thickness of each functional layer,an ideal low-voltage high-performance red OLED device was obtained.The main tasks are as follows:Firstly,high efficiency red phosphorescent material PQ2Ir(dpm)was selected as emitter and materials m CP and Cz Si were selected as host materials.In order to improve the hole injection and transfer ability to lower the injection barrier between the anode and hole transport layer and improve the carrier's balance within light-emitting layer(EML),material HAT-CN was selected to modify ITO surface for improving the transport of holes.Through the EL performances and EL spectrum of these devices,the performances of the devices with different structure were further analyzed.The results show that the performances of the single-EML devices doped with m CP as host material is better than that of the double-EMLs devices doped with m CP and Cz Si as host material.Finally,the optimized single-EML device with driving voltage,maximum brightness,external quantum efficiency,current efficiency and the maximum power efficiency up to 2.8 V,23710 cd /m2,14.82%,23.05 cd /A and 24.97 lm/W,respectively.Even at the brightness of 1000 cd /m2,the driving voltage is only 4.3V.Then,we selected another bipolar material BUPH1 as host material for red phosphor material PQ2Ir(dpm)and prepared single-EML devices.Under the condition of ensuring the low driving voltage of devices,we fabricated double-EMLs devices with hole transmitting material Tc Ta as host material.Through the design and optimization of the device structure,high performances devices with low driving voltage were obtained.Finally,the optimized device with maximum brightness,external quantum efficiency,current efficiency and the maximum power efficiency of 2.3 V,29870 cd /m2,12.18%,19.74 cd /A and 25.84 lm/W,respectively.At the brightness of 1000 cd /m2,the driving voltage is as low as 3.4V.