High-Performance Organic White Light Devices And Design,Properties Of Novel Blue Phosphorescent Complexes

WOLED is one of the most promising new lighting technologies.It has many advantages such as ultra-thin,flexible,adjustable light color and friendly to human eyes,but its efficiency under high brightness can not compare with LED(Light-Emitting Diode),and there is still a certain gap between them.In order to improve the efficiency of WOLED devices,one of the main strategies at present is to prepare fluorescent-phosphorescent hybrid WOLED devices.Generally,blue light materials use a classic fluorescent system to provide better blue color purity.For the light color of long wavelength,phosphorescent materials are used.This is because phosphorescent material can simultaneously capture the triplet and singlet excitons generated by electro-excitation,achieve 100%internal quantum efficiency and maximize the electroluminescence efficiency of WOLED devices.In view of the above problems,in this article,a high-performance fluorescent-phosphorescent hybrid white light device based on blue fluorescent host was fabricated,and two new series of blue phosphorescent iridium complexes with different spectral characteristics were designed and synthesized.The color purity of the blue phosphorescent material is improved by suppressing the long-wavelength shoulder and eliminating the long-wavelength shoulder,respectively,while those materials of two series have high electroluminescence efficiency.This work provides more material to support full phosphorescent organic white light devices.The details are as follows:1.The blue fluorescence emission is provided by the classical blue fluorescent molecule Bepp2(acts as a host material at the same time),a green phosphorescent molecule FPPCA with double carrier transport property is used to penetrate the double luminescent layer,which is used as the host of the red phosphorescent guest molecule BZQPG as well as the guest of the blue fluorescent host molecule Bepp2,a double-layer,three-color(blue,green,red)warm white light device with simple structure was prepared.The device achieves efficient energy transfer between phosphorescent-phosphorescent molecules(PPT)as well as fluorescent-phosphorescent molecules(FPT).This WOLED can achieve a relatively high EQE value of 27.3%at a luminance of 1000 cd m-2.The power efficiency can reach 74.5 lh W-1,the Color Rendering Index(CRI)is up to 85,and a warm white light emission without eye injury is achieved.The Commission Internationale de L,Eclairage(CIEx,y)coordinate is(0.43,0.46),and the device exhibits the Wgh efficiency and high CRI required for the actual solid state illumination at the same time,and it is one of the best performances of WOLED available today.2.Using a strategy of inhibiting or weakening the shoulder emission(3LC dominant)to improve the purity of blue light,a fluorinated phenylpyrinidine ligand was designed as chelating ligand,and trifluoromethylpyridine triazole was used as auxiliary ligand,highly efficient phosphorescent molecules(sFpmy)2lrfmptz(Ira),(dFpmy)2Irfmptz(Irb)and(tFpmy)2Irfmptz(Irc)were prepared.In the T1 composition of the three molecules,the ratio of3LC was less than 29%.Due to the difference in the number of fluorine atoms and the position of substitution,the three phosphorescent molecules have a regularity of change in the maximum emission wavelength,relative intensity of the shoulder,FWHM,CIEx,y,and luminous efficiency.The introduction of a fluorine atom in the para position of the benzene ring of the chelating ligand can significantly inhibit the shoulder in the phosphorescence spectrum of the complexes,and the shoulder intensity in the electroluminescence spectrum is lower than 70%of the main peak.The introduction of two fluorine atoms at the 2,4 position of the benzene ring,respectively,can significantly shift the peak position of the phosphorescence spectrum to a bluer region,and the electroluminescent devices prepared by using these compounds as emitters achieve high efficiency,in which the peak EQE of the trifluoride is close to 30%.This part of the research has certain significance for further improving the spectral quality of the blue phosphorescent molecules based on phenylpyridine and theirs further application in WOLED.3.Using the strategy of eliminating shoulder(single peak emission,3MLCT dominated)and narrowed spectrum(3LC dominant)to improve the purity of blue light,three sky-blue phosphorescent molecules(Medfpypy)2IrPy(Ir1),(dfpypy)2IrPy(Ir2)and(Medfpypy)2IrDMPy(Ir3),with guanidinate pyrrole as an auxiliary ligand were designed and prepared.The series of blue phosphorescent molecules are single-peak emission,and the narrowest FWHM is 53 nm after methylation modification of the pyrrole group.Theoretical calculations show that the triplet transition of the material system mainly comes from HOMO(Highest Occupied Molecular Orbital)-LUMO(Lowest Unoccupied Molecular Orbital).The guanidinate-pyrrole auxiliary ligand ensures that the high separation of HOMO and LUMO orbital distribution,and also increases the composition of 3ML/LLCT in the triplet transition,while the ration of 3LC is reduced,this is the key factor for achieving a narrow emission with only a single peak.The work of this part has a strong practical significance for the design of blue phosphorescent complex molecules with single and narrow peak emission based on phenylpyridine chelating ligands.In summary,in this paper,we have prepared a simple two-layer,three-color(blue,green,red)warm white light device with a blue fluorescent molecule Bepp2,a green phosphorescent molecule FPCCA,and an orange-red phosphorescent molecule BZQPG,using a fluorescence-phosphorescence hybridization strategy.Efficient energy transfer between Bepp2 and FPCCA as well as FFPCA and BZQPG,can achieve a fairly high EQE value of 27.3%under the brightness of 1000 cd m-2,and the power efficiency of 74.5 lm W-1 can also be reached.CRI is up to 85,CIEx.y coordinate is(0.43,0.46),a warm white light emission that is friendly to the human eye is achieved.In order to further obtain more standard white light,we focus on improving the intensity of blue light in the spectrum,and replacing the inefficient traditional fluorescent molecule Bepp2 with a more efficient blue iridium complex.The chelated ligand used is the most widely studied phenylpyridine-based derivative,which makes the relevant research conclusions maximize the applicability for the blue iridium complex,and plays a greater role in promoting the development of the blue phosphorescent material.Specifically:(1)using a strategy of inhibiting or weakening the shoulder emission,using fluorinated phenylpyrimidine as a chelating ligand,and designing Ira,Irb and Ire with trifluoromethylpyridine triazole as an auxiliary ligand,in which,the shoulder emission of Ira and Irb is weak in dichloromethane solution,and the shoulder emission intensity of Ira is most inhibited in the electroluminescence spectrum,and its relative intensity is lower than 70%of the main peak.In addition,we have studied the crystal structure,photophysical properties and composition of T1 of Ira,Irb and Ire in detail,and summarized the spectral changes and luminescence properties of three molecules;(2)based on the inhibition of shoulder emission,this work further adopted the strategy of eliminating shoulder emission.Three high-efficiency phosphorescent molecules Ir1,Ir2 and Ir3 with guanidinate pyrrole as an auxiliary ligand were designed and prepared.All of them are single peak emission,in which the narrowest FWHM is achieved after the methylation of the pyrrole group,which is 53 nm.We also have studied the crystal structure,photophysical properties,and T1 composition of these three molecules.Fine studied and summarized spectral variation regulation and luminescent properties of three molecules.Research above make a contribution to design of blue phosphorescent iridium complex and the preparation of WOLED.