| Organic light emitting diodes(OLEDs)have huge potential applications in flat panel display,solid state lighting and LCD backlight due to their light weight,thin thickness,high brightness,high efficiency,environmental protection,flexible display and so on.The world's major OLED manufacturers and researchers have invested a lot of efforts in the research and marketization of OLED,and OLED is regarded as the new generation display technology.General speaking,white OLED(WOLED)can be realized by complementary color or three primary colors.Device efficiency has been limited by the inefficiency of blue light materials.Therefore,in the process of exploring WOLED based on deep blue materials,we improve its defect through more reasonable device structure design leading to achieving high performance in white lighting emission.Firstly,we have prepared a series of white organic light emitting diodes with double-emitting layers and explored the performance of deep blue phosphorescent materials.PO-01 and Fir6 are serviced as yellow phosphorescent materials and blue phosphorescent materials,respectively.Considering that the mixed-host structure not only balances the transport of holes and electrons in the light-emitting layer but also expands the exciton distribution area and improves devices performance,we have optimized the blue light emitting layer with it.On this basis,we adjusted the thickness of yellow emitting layer and achieved best efficiency of 33.1cd/A(24.9lm/W)with good spectral stability and a slightly change in color coordinates of(0.01,0.01).Next,in order to further optimize the devices,we adjust the doping ratio of the mixed host.When mCP:CBP(2:3)is used in device H,the maximum efficiency is 38.2 cd/A and26.4 lm/W.The current efficiency of the device can still maintain 35.6 cd/A and 30.2cd/A in a wide range of brightness from 1000 cd/m~2 to 5000 cd/m~2,showing excellent efficiency roll-off.In general,devices performance and the spectral stability have been greatly improved.In addition,WOLEDs fabricated with all-phosphorescent materials is to be improved in color coordinates and device lifetime.Hybrid WOLEDs consisted of fluorescent blue emitters have garnered growing attraction for their harvesting of both singlet and triplet excitons.Then,we explored the new deep blue fluorescent material L-BPPI and designed related experiments to optimize its devices performance.Firstly,we optimize the thickness of L-BPPI.Then,Hybrid WOLEDs are prepared to the next experiment.CBP was used as a spacer layer between the two emitting layers to adjust the balance of excitons.The yellow emitting material was still selected as PO-01 and the devices achieved good performance.Besides,a suitable ratio of hybrid spacer was used in place of CBP between the yellow and blue layers.The prepared two-color WOLEDs exhibited a fairly stable white emitting spectrum with a peak efficiency of40.7 cd/A(26.8 lm/W).Finally,we further inserted the ultra-thin red phosphorescent layer in both sides of the middle layer respectively to achieve two three-color WOLEDs.The devices demonstrated a maximum efficiency of 35.3 cd/A(25.4 lm/W)and a very low efficiency roll-off. |
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