Study On Material Synthesis And Photoelectric Property Of High Efficiency And Stable Blue OLEDs

Since the invention of organic electroluminescent diodes?OLEDs?,great progress has been made in both materials and devices in the past 30 years.In terms of commercial applications,OLEDs have gradually become market-oriented and large-scale in the field of information display,and have also entered the fast lane of industrialization in the field of solid-state lighting and flexible displays.Although it already has the industrialized technology foundation,OLED technology has not reached perfection,and it still needs to be perfected in some technical aspects.This has also attracted much interest.This thesis focuses on the current technical bottlenecks of OLED that need to be solved,and has always carried out research work on blue OLEDs.The research objects of this thesis focus on the blue light-emitting layer?EML?,including the host material and different types of light-emitting guest materials,especially the blue light guest material,occupying the vast majority of the thesis's length.In the study of blue-light guest materials,we have systematically studied three generations of luminescent materials that OLEDs are currently undergoing,including deep-blue fluorescent material?fluorophor?,long life-time phosphorescent materials?phosphor?,and new types of highly efficient thermally excited delayed fluorescent materials?TADF?.By comparing the advantages and disadvantages of different types of materials,continuous improvements have been made in both materials and devices to achieve high efficiency and long life-time blue-OLEDs.The details of the specific chapters are as follows:?1?In chapter 1 and 2,we introduced the research history,working principle and development status of OLED.The photophysical process and the influencing factors of the luminous efficiency in the luminescence process are fully analyzed,and the physical meanings of various parameters of the OLED device are also explained in detail.In terms of materials,we have introduced three generations of OLED luminescent materials,especially the TADF materials that have emerged in recent years.The TADF materials are introduced in detail according to different accept units.?2?In chapter 3,we studied the novel exciplex-based host materials that are currently very promising,and focused on the relatively scarce acceptor materials of blue exciplex.By controlling the number and linkage-position of the phenyl phosphine oxide?PPO?unit to prepare two types of electron acceptor molecules,with wide bandgaps and deep HOMO energy levels.Furthermore,we used the promising method of solution-process.We successfully achieved two blue-light exciplex by the method,and we developed blue-phosphorescent OLED devices based on these two exciplex as the host exhibit excellent device efficiency and less efficiency roll-off.?3?In chapter 4,we studied the traditional fluorescent materials that once again attracted the attention of the academic field.In order to realize deep blue light emission and avoid red-shift effect,we synthesized two novel deep-blue fluorescent emitters by introducing a relatively rigid unit and connected with two classic blue emission units.Both the introduced rigid moiety and the classical moiety can form a large dihedral angle and successfully overcome the effect of aggregated red-shift in the thin film state.Like the previous chapter,we also optimized the device fabrication and chose a simple non-doped OLEDs without any hole-injection layers,and successfully obtain a high efficiency deep-blue OLED with a small efficiency roll-off.?4?In chapters 5 and 6,we studied two types of blue phosphorescent iridium?III?complexes.In Chapter 5,we have prepared a blue homogenous Ir?III?complex based on benzimidazole[1,2-c]quinazoline units by a very simple and effective synthesis method.The device life-time(T₆₅)based on the new emitter up to 165 h at an initial brightness of 1000 cd/m².In Chapter 6,we continue the study of long life-time blue phosphorescent materials.We derive the ligand of imidazophenanthridine units,retained the functional group at the 3-position of the imidazophenanthridine unit,introduced a new reaction site at 7-position and introducing the methyl,ethyl and isopropyl groups.Subsequently,three iridium-based complexes were prepared with these three ligands.We prepared the long life-time blue devices based on these complexes,and the longest life-time(T₅₀)of the devices was 446 h at an initial luminance of 1000 cd/m².Then,we discussed the intrinsic reasons why the types of complexes show such good device stability.Finally,the photo-degradation mechanism was further investigated.?5?In Chapter 7,we focused on the study of high efficiency blue-emitting TADF emitters.We developed two donor units based on indeno[2,1-b]carbazole and3-?fluoren-3-yl?-carbazole.By introducing a methyl group to increase the spatial angle between the donor and acceptor,reducing the overlap of HOMO and LUMO distribution to achieve smaller?E_ST.Both of the TADF devices using them as guest materials exhibit high device efficiency.In order to further develop the application potential of the material,we also studied the different device performances of sensitizing monochromatic phosphorescent emitters and TADF emitters as host materials.Subsequently,we further studied the two-color TADF-phosphorus hybrid white OLED device with single EML where the TADF emitter was simultaneously used as the host and the blue guest material.Both of the monochromatic devices and the hybrid white OLED device achieved high external quantum efficiency.