High-efficiency Red Phosphorescent Organic Light-emitting Diodes Based On Bipolar Host And Optimization Of Their Performance

Since its introduction,organic light-emitting diodes(OLEDs)have been developing rapidly and are widely used in flat panel displays and lighting,and have attracted considerable attention in the industrial world.The world's major companies have taken a proactive approach to the development of organic light-emitting diodes,further promoting the rapid development of organic light-emitting diodes.It is well known that the theoretical internal quantum efficiency of fluorescent OLEDs is only 25%,while phosphorescent OLEDs capture all single-state and triple-state excitons by enhancing inter-system crossover(ISC)through the heavy atom effect,which can theoretically reach 100%internal quantum efficiency and make full use of excitons,which is undoubtedly exciting and good news.Therefore,the research on phosphorescent OLEDs is gaining more and more attention from researchers.For phosphorescent OLEDs,the host-guest system of the emitting layer is crucial,requiring both a good emitting guest material and a matching host material.Although monopolar hosts,such as4,4'-bis(carbazol-9-yl)biphenyl(CBP),have been shown to match the phosphorescent guest material well and obtain high external quantum efficiency(EQE)values,the narrow complex region near the interface in the emitting layer may lead to rapid efficiency roll-off,thus compromising device stability.By screening suitable bipolar host materials synthesized from electron donor groups and electron acceptor groups,it has been shown in phosphorescent organic light-emitting diodes(PHOLEDs)to facilitate the balance of hole and electron injection and transport,broadening the complex region and thus mitigating the efficiency roll-off and maintaining stable device performance.Bipolar phosphorescent host compounds can facilitate charge injection,balance carrier transport rates,and enhance device efficiency to reduce efficiency roll-off.1.The electron donor group and acceptor group are the key parts of organic light-emitting compounds.In this paper,a bipolar main host material named DTBDQ was developed using the donor group dibenzothiophene group and the acceptor group dibenzo[F,H]quinoxaline.The introduction of two nitrogen atoms into the dibenzo[F,H]quinoxaline molecule increases the electronegativity,the LUMO energy level and the HOMO energy level become deeper,and it is an electron acceptor group with almost no change in the trilinear state energy level.Dibenzothiophene is the hole-transporting group,and the two groups are connected by two interstitial benzenes to obtain DTBDQ,which has a higher trilinear state energy level.The prepared red phosphorescent organic light-emitting diodes have excellent performance with a peak external quantum efficiency of 19.79%,a peak current efficiency(CE)of13.51 cd A^-1and a peak power efficiency(PE)of 14.44 lm W^-1,with a rolling decrease in efficiency and an EQE of 18.08%at a luminance of1000 cd m^-2.2.A dual-host material is used to meet the higher performance requirements,and the effect of different host ratios on the efficiency of red light devices is experimentally explored.We use DTBDQ and CBP as dual-host,and vary the percentage of CBP to obtain the best device performance.The best device efficiency was obtained experimentally when the percentage of CBP was 30%.The double-host material regulates the carrier transport rate,which makes the electron and hole rates injected into the light-emitting layer more balanced and improves the exciton utilization.The current efficiency and external quantum efficiency of the prepared devices are 13.14 cd A^-1and 17.77%,respectively.