Synthesis,photophysical Properties Of Hyperbranched White Polymers Based On Poly(9,9-dioctylfluorene) For Organic Light Emitting Devices

In recent years,white organic light-emitting devices(OLED)have been developed rapidly in the field of display and lighting owing to their unique merits,including flexiblity,transparentness,thinness.Excellent results have been achieved in the field of white OLED for decades from the experimental stage to the industrial stage.However,good efficiency stability of white OLED is deficient and the preparation process is complex,which restricts its application and development,currently.Herein,we synthesized three types of hyperbranched white OLED polymers based on poly(9,9-dioctylfluorene)(PFO).In addition,we prepared single-active-layer OLED devices,accompanied by analyzing the relationship between structure and performance.The main research contents contains three parts as follow.1.To solve the problem of poor efficiency stability of linear white-light OLED polymers,a series of three-color hyperbranched white-light OLED polymers PFFOxRy were designed and synthesized.These hyperbranched white-light OLED polymers contained tris[1-phenylisoquinolinato-C2,N]iridium(III)(Ir(piq)3)as the red emission cores,and PFO with insertion of green fluorescent units of fluorenone(FO)as blue emission branches.These polymers PFFOxRy showed high fluorescence quantum efficiency(higher 60 % in solution and 28.1 % ~ 47.2 % in neat films)and excellent thermal stabilities(Tg>135 oC).White-light OLED Px were fabricated with polymers PFFOxRy as single active layer.Based on comparative analys is,the electroluminescent(EL)performances of device P2 was the best with FO content of 0.05 mol% and Ir(piq)3 content of 0.1 mol%,,showing a maximum current efficiency of 3.85 cd/A,a maximum brightness of 3354 cd/m~2(@ 10.9 mA/cm~2)and a high color rendering index(CRI)of 87.While it showed obvious roll-off phenomenon at high current density.2.To solve the problem of the influence on device efficiency stability by aggregation-caused quenching(ACQ)of white-light OLED polymers,a series of hyperbranched white-light OLED polymers PFTPE-Rx were designed and synthesized,with Ir(piq)3 as the red emission cores,PFO with insertion of AIE units of TPE as cyan emission branches.These polymers PFTPE-Rx exhibited favorable AIE properties.There was no fluorescence emission in a good solvent,while with the addition of poor solvent,fluorescence emission gradually increased.White-light OLED Rx were fabricated with polymers PFTPE-Rx as single active layer,which showed well efficiency stability and no obvious roll-off at high current density.Based on comparative analysis,the EL performances of device R2 was the best with Ir(piq)3 content of 0.5 mol%,showing a maximum current efficiency of 2.43 cd/A,a maximum brightness of 4686 cd/m~2 and a high CRI of 86.3.To investigate the influence regularity of EL performances from the different position of TPE in polymer,a series of hyperbranched white-light OLED polymers PFGxRy with TPE as the cores,PFO inserted red emission groups Ir(piq)2(acac)as the blue emission branches were designed and synthesized.These polymers PFGxRy did not show AIE properties,because the benzene rings of TPE were fixed and could not rotate in good solvent.White-light OLED Tx were fabricated with polymers PFGxRy as single active layer.Devices Tx showed obvious roll-off at high current density comparing to device Rx,which proved that the introduction of AIE groups could effectively enhance the efficiency stability of the device.Based on comparative analys is,the EL performances of device T3 was the best with TPE content of 5 mol% and Ir(piq)2(acac)content of 0.5 mol%,showing a maximum current efficiency of 5.29 cd/A(@ 23.46 mA/cm~2),a maximum brightness of 9473 cd/m~2.