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Photoluminescent properties of advanced / LMW phosphorescent materials

wallpapers News 2020-08-03

white organic light emitting diode (wold) as a planar light source with no blue light harm no glare flexible bending other unique properties is considered to be the future star of solid-state lighting. High efficiency long life are the basic requirements for large-scale application of WOLED in lighting industry but at present it is still difficult to achieve high performance WOLED in high brightness. Nowadays high efficiency WOLED structures are generally based on all phosphorescence. Phosphorescent materials usually have strong spin orbit coupling effect which can make full use of singlet triplet excitons. Therefore all phosphorescent WOLED was once considered as the most promising white light solution to promote WOLED industrialization. However due to the lack of efficient stable blue phosphorescent materials the short life of all phosphorescent WOLED has not been well complemented which can not meet the practical requirements. Therefore the yellow or green or red phosphorescent guest the blue phosphorescent guest hybrid fluorescent phosphorescent WOLED (HY OLED) become a compromise choice. However this kind of structure design is limited by the natural characteristics of low exciton utilization of traditional fluorescent objects which makes it difficult to design stable efficient WOLED structure.

in order to design a high-performance wold device structure Professor Feng Minqiang of FUNSOM of Soochow University proposed a four-color fluorescent phosphorescent hybrid wold device structure design. The wold prepared by this method showed excellent electroluminescent performance with the maximum external quantum efficiency (EQE) power efficiency (LE) of 42.9% 66.3% respectively lm/W。 The device keeps 40.5% (53.4 LM / W) at 1000 CD / m2 the performance roll off is very small. By using high refractive index substrate imprinting ideal microlens array structure we further improve the efficiency lifetime of the device. Finally the EQE le of series WOLED are 126.1% 150.7 LM / W respectively at 1000 CD / m2 the CRI is close to 80. In addition we have done accelerated aging test on white light device. The T50 of the device without light extraction can reach 140 hours when the initial brightness is 10000 CD / m2. After conversion the life of the device with light extraction can reach 12600 hours (T50: the time when the brightness is reduced from the initial value l0 = 1000 CD / m2 to 50%). The newly designed four-color WOLED device structure consists of a yellow red light emitting unit (yru) with exciplex as the main body a blue red light emitting unit (BRU) with TADF as the blue light emitting material. In this structure TADF materials have various effects in the series structure: (1) intermolecular TADF materials (exciplex) as the main body of yru (2) TADF materials as the luminescent guest of blue light (3) the above-mentioned TADF blue light guest is used as the auxiliary host to sensitize the red phosphorus light guest material in the luminescence layer. This method has the following advantages: firstly the exciplex body is introduced into yru which can eliminate the injection barrier from the charge transfer layer to the light-emitting layer reduce the driving voltage. In addition TADF material is used as sensitizer in bru yru to reduce the doping concentration of phosphorescence thus reducing the preparation cost. Then by controlling the concentration of red phosphorescent guest in bru the proportion of energy transfer from blue phosphorescent guest to red phosphorescent guest can be adjusted so that the white light spectrum can be adjusted in a larger range. Finally we design a multi-channel radiation attenuation bru to replace the traditional blue light unit (BU) so that excess blue excitons can be transferred to the red light object. This process can further improve the stability of the blue light unit at high brightness. In short the structure has a good balance between efficiency stability. The researchers believe that this research not only provides an effective preparation scheme for WOLED with high performance long life but also reveals the potential of WOLED combined with TADF material design device design light extraction technology as a high efficiency long-life low-cost solid-state lighting source.


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