Research On Energy Transfer And Luminescence Mechanism In Doping OLED Devices

With the development of technology and the improvement of living standard,people's requirements for the color quality of panel displays are higher and higher,thus the organic light emitting diodes?OLED?that fulfills the requirement has captured our eyes gradually.Due to numerous properties such as self-emitting,high contrast,wide color gamut,quick response,wide viewing angle,low power consumption,thin structure and flexibility,OLED products achieve unanimous appraise after launching the market,many people even call it as the“Ultimate Display”.With the application of OLED in consumer electronics field,it has become the new development trend in display field.Although the technology of OLED has achieved great progress,the device efficiency is still need to be improved,so the research on developing novel device structure and its mechanism reveal are still valuable.This paper mainly concentrates on the energy transfer and luminescence mechanism and it is divided to three parts:Firstly,double doping method was used to fabricate fluorescent OLED and its influence on the performance of solution processed OLED was investigated.Experiment results indicated that the current efficiency of double dopants OLEDs achieved one time enhancement compared with the single dopant devices.To study the effects of the doping ratio on device performance,three kinds of double dopants devices were fabricated and a comparison was made on their performance.Then we investigated the luminescence mechanism in different devices by analyzing the device spectra,the result indicated that the luminescence characteristics in double dopants devices were decided by the dominant dopant.At the same time,via analyzing the I-V curves of double dopants devices and their corresponding hole-only or electron-only devices,the result indicated that the enhancement of device efficiency to the improvement of charge balance,which was improved after adding the second dopant.Considering that the double doping method could improve the current efficiency,we believed that this method can be used to increase OLED efficiency.Secondly,we chose CBP as the host material,thermally activated delayed fluorescence material 4CzIPN as the assistant dopant and red phosphor Hex-Ir?phq?₂?acac?as the guest material to fabricate a novel co-doping device.An efficient assistant dopant system was constructed after optimizing the doping ratio.In this system,energy was transferred from the host or assistant dopant to the guest material through Forster energy transfer process and it would greatly enhance the brightness and lower the turn-on voltage.Meanwhile,by analyzing the spectrum characteristics and roll-off phenomenon variation in different 4CzIPN doping ratio,we investigated the effect of assistant dopant system on the energy transfer process and luminescence mechanism in devices.Through further analysis about the exciton generation mechanism,the improvement of roll-off was attributed to the broadening of charge recombination region and the reduction of triplet-triplet annihilation.This research provided a new pathway of fabricating stable OLEDs with simple device structure.Finally,this article studied the influence of 4Cz IPN as the assistant dopant on the operation lifetime of phosphorescent OLEDs.Compared with conventional device in which CBP was used as the host material,these devices achieved great enhancement in device lifetime.By analyzing the film crystallization property and energy transfer mechanism of devices with different structures,we suggested that the excellent stability of devices should be attributed to the variation of crystallization property in mixed film,the broadening of charge recombination area and the reduction of triplet-triplet annihilation.Meanwhile,the device structure needed to be optimized to achieve better device performance,in order to fabricate more efficient and stable phosphorescent OLEDs,further optimization of the device structure was needed in the future.