The White Organic Light-emitting Diodes(WOLEDs)Based On Blue Emission Thermally Activated Delayed Fluorescence

In recent years,the performance of organic light-emitting diodes(OLEDs)has been greatly improved and some OLED products have been commercialized.However,in order to completely replace inorganic light-emitting diodes(LED),white organic light-emitting diodes(WOLEDs)need to be ameliorated in many aspects,such as device efficiency,device structure,fabrication technology and cost.In this thesis,the structure of WOLEDs was designed and optimized based on the blue thermally activated delayed fluorescent material(TADF)with AIE characteristics,and a series of high-efficiency fluorescent/phosphor hybrid and full-fluorescent WOLEDs were successfully fabricated under the condition of simplifying the devices structure,fabrication technology and reducing the cost.The specific research works of this thesis are as followsFirstly,the blue TADF material m-ACSO2 with yellow phosphorescent material PO-01 was combined to fabricate a series of doped fluorescent/phosphorescent hybrid WOLEDs.It is worth noting that m-ACSO2 is a blue emitter and a host of PO-01 simultaneously.Therefore,compared with the traditional double-doped WOLEDs,the structure of the white devices in this work is not only simple and efficient,but also avoids the use of other host materials.The maximum power efficiency,current efficiency and EQE of the optimized WOLEDs are 64.3 lm/W,61.4 cd/A and 20.9%,respectively.Then,the phosphorescent ultrathin emitting layer(UTL)structure was introduced and combined with blue TADF material 2tCz2phCzBn to fabricate a series of non-doped fluorescent/phosphorescent hybrid WOLEDs.In this work,we firstly took PO-01 as yellow phosphorescent UTL and investigated the effect of the position of PO-01 UTL on the performance of complementary white devices.For the optimized complementary WOLEDs,the maximum power efficiency,current efficiency and EQE are 67.01m/W,51.2 cd/A and 19.3%,respectively.Moreover,the CIE coordinates and CRI at the luminance of 1000 cd/m2 are(0.398,0.444)and 57,respectively.Secondly,we took Ir(ppy)2(acac)and Ir(MDQ)2(acaca)as green and red phosphorescent UTL respectively,and studied the effect of the thickness of red UTL on the performance of three primary-color white devices.The best WOLEDs showed a high power efficiency of 48.3 lm/W,a current efficiency of 36.1 cd/A and a EQE of 16.6%.Besides,the CIE coordinates and CRI at the luminance of 1000 cd/m2 are(0.37,0.43)and 82,respectively.Compared with the traditional host-guest emitter system,the use of non-doped UTL could further simplify the device structure and reduce the cost.Finally,the phosphorescent UTL was replaced with orange-red TADF(3DMAC-BP)UTL,and the fluorescent UTL was combined with m-ACSO2 to fabricate non-doped full-fluorescent WOLEDs.At the same time,we studied the effect of the position of 3DMAC-BP on the performance of the devices.The maximum power efficiency,current efficiency and EQE of the optimized WOLEDs are 46.4 lm/W,51.7 cd/A and 24.2%,respectively.Besides,the CIE coordinates and CRI at the luminance of 1000 cd/m2 are(0.41,0.43)and 81,respectively.More importantly,only three organic materials are used,which can further simplify the device structure.In addition,the adoption of TADF UTL can further reduce the cost.