Design and Systhesis of Dianthracenylphenylene-based Deep Blue Emitters for Organic Light-emitting Diodes

Author:Peng Ling

Supervisor:zhu xu hui


Degree Year:2019





With the advantages of high efficiency,low energy consumption,self-luminescence,wide viewing angle,ultra-thin,lightweight and flexibility,organic light-emitting diodes(OLEDs)are leading the development of information display and lighting technology.The development of high efficient and stable deep blue emitters will further promote the application of OLEDs.Compared with classic organic fluorescent materials,triplet-triplet annihilation(TTA)fluorescent materials have received considerable attention due to achieving up to 62.5%internal quantum efficiency in organic light-emitting diodes(OLEDs).In this dissertation,we intend to develop high-performance TTA-based deep blue emitters with CIE y≤0.08 from a chemical perspective.Consequently,a series of dianthracenylphenylene-based blue emitters has been designed,synthesized and characterized for OLEDs.The main findings are presented below.1)By introducing solubilizing 3,5-di(4-t-butylphenyl)phenyl moiety at the one end and different electron-deficient/withdrawing groups at the other end,we have obtained deep blue emitters DAPPy,DAPBN and DAPPQ based on the highly twisted dianthracenylphenylene unit.All the compounds show high thermal decomposition temperatures over 430 oC(defined at 1%weight loss)and glass transition temperatures over 220 oC.The characterization of the OLEDs(ITO/HATCN(15 nm)/TAPC(60 nm)/TCTA(10 nm)/EML(20 nm)/TPBi(40nm)/LiF(1 nm)/Al)that utilized these nondoped emitters provided high external quantum efficiencies(EQEs)of(4.6-5.9)%with low efficiency roll-off and Commission International de L’Eclairage(CIE)coordinates(0.15,0.07),(0.15,0.08)and(0.15,0.09),respectively.The analysis of the EL transient decay revealed that TTA contributed to the observed performance.Due to the enhanced fluorescence quantum efficiency in solid state and electron mobility,the DAPBN OLED exhibited the highest EQE of 5.97%@1298 cd m-2.Moreover,DAPBN was explored as a dopant emitter in the OLEDs with Phen-m-PhCz as the host.The OLED efficiency gradually improved with increasing the dopant concentration,which was accompanied by decreasing efficiency roll-off,largely due to the enhancement of TTA effect.2)It has shown that utilizing a conventional fluorescent dopant emitter into a TTA host to afford a blend emitting layer has led to high-efficiency and stable blue OLEDs.In this context,we fabricated doped sky blue OLEDs with the structure of ITO/HATCN(15nm)/TAPC(60 nm)/TCTA(10 nm)/DAPPy or DAPBN:DSA-Ph(20 nm)/TPBi(40 nm)/LiF(1 nm)/Al.DSA-Ph is a conventional fluorescent dopant emitter.Due to the combined effects involving the TTA host materials and effective F?rster energy transfer between the host and dopant emitter,the DAPPy:1%DSA-Ph OLED showed a maximum CE of 13.04 cd A-1@27100 cd m-2(corresponding to 8.78%EQE)with CIE coordinate(0.14,0.20).By contrast,the DAPBN:1%DSA-Ph OLED produced a maximum CE of 15.30 cd A-1@43100 cd m-2(corresponding to 9.71%EQE)with CIE coordinate(0.15,0.22),which is among the most efficient DSA-Ph based sky blue fluorescent OLEDs.It should be noted that the OLED efficiency gradually decreased as increasing the dopant concentration from 1%to 5%.For instance,the maximal DAPPy or DAPBN:5%DSA-Ph OLED efficiency reduced to 7.67%and 8.16%,respectively.3)Based on DAPBN in Chapter 1,dianthracenylphenylene-based blue fluorescent emitters DAPBN1 and DAPBN2 were further designed and synthesized,which have a3,5-diphenylphenyl moiety at the one end and 4-cyanophenyl or3,5-bis(4-cyanophenyl)phenyl group at the other end,respectively.Both compounds show a high Td of 427 and 488 oC(at 1%weight loss)and Tg of 199 and 231 oC,respectively.The characterization of the nondoped OLEDs with the structure of ITO/HATCN(15 nm)/TAPC(60 nm)/TCTA(10 nm)/DAPBN1 or DAPBN2(20 nm)/TPBi(40 nm)/LiF(1 nm)/Al revealed maximum external quantum efficiencies of over 5%with CIE coordinates(0.14,0.11)and(0.14,0.10),respectively.Remarkably,the DAPBN2 OLED showed a higher CEmax/EQEmaxax of 4.83 cd A-1/5.45%@1348 cd m-2,due to its increased electron mobility;more significantly,the EQE slightly reduced to 5.11%@5000 cd m-2,exhibiting small efficiency roll-off.