Study On The Low Efficiency Roll-off Organic Light-emitting Diodes Based On Acridine Heterocyclic Derivatives

Organic light-emitting diodes?OLEDs?have the advantages of self-illumination,fast response,wide color gamut,strong contrast,wide viewing angle,and low power consumption etc.,which are the future development trend of the displays and solid-state lighting.Aiming at the key issues of cost and stability of OLEDs,three novel organic materials based on acridine heterocyclic derivatives,Ip Cm-Ph Bz Ac?1,3-?4-?12,12-dimethylbenzofuro[3,2-b]acridin-7?12H?-yl?phenyl?6-isopropyl-4H-chrom-en-4-one?,Dp An-Bz Ac?2,10-?4-?12,12-dimethylbenzofuro[3,2-b]acridin-7?12H?-yl?phenyl?-10-phenylanthracen-9?10H?-one?and Dp Trz-Bph Bz Ac?3,7-?40-?4,6-diphenyl-1,3,5-triazin-2-yl?-[1,10biphenyl]-4-yl?-12,12-dimethyl-7,12-dihydrobenzo-furo[3,2-b]acridine?have been designed and synthesized in this dissertation.We have investigated their optoelectronic characteristics with a deep discussion into the electroluminescence?EL?characteristics and efficiency roll-off of related devices using these materials as emitters.The main research results have been made which follows.First,three newly materials Ip Cm-Ph Bz Ac,Dp An-Bz Ac,and Dp Trz-Bph Bz Ac have been successfully designed and synthesized using Ip Cm,Dp An,and Dp Trz as electron acceptors and Bz Ac as electron donors,respectively.These three materials show good thermal stability,and the T_gof Dp An-Bz Az and Dp Trz-Bph Bz Ac are 137and 148?,respectively.They can form uniform amorphous films with high morphological stability.Dp An-Bz Ac and Dp Trz-Bph Bz Ac exhibited better thermally activated delayed fluorescence?TADF?characteristics and higher photoluminescence quantum yield?PLQY?,which were 76.3%and 90.3%,respectively.And Dp Trz-Bph Bz Ac has a small singlet-triplet state energy gap difference(?E_ST)of 0.17 e V.Excellent properties indicate that they have bright prospects in the application of luminescent materials.Next,the EL characteristics of Ip Cm-Ph Bz Ac,Dp An-Bz Ac,and Dp Trz-Bph Bz Ac were investigated as host materials,and the efficiency roll-off was discussed.Compared with the traditional material 1,3-bis?carbazolyl?benzene?m CP?,the three Ip Cm-Ph Bz Ac,Dp An-Bz Ac,Dp Trz-Bph Bz Ac have good carrier transport balance characteristics,of which Dp Trz-Bph Bz Ac has better bipolarity.We have fabricated Ph OLEDs using green bis?2-phenylpyridine?iridium?III?acetylacetonate as doped emitters and Ip Cm-Ph Bz Ac,Dp An-Bz Ac,Dp Trz-Bph Bz Ac as host materials in two single and double hosting schemes.The results show that Ip Cm-Ph Bz Ac,Dp An-Bz Ac,Dp Trz-Bph Bz Ac can be used as the host materials.The Ph OLEDs with the single host system of Dp An-Bz Ac and Dp Trz-Bph Bz Ac exhibit low turn on voltages of 2.2 V and2.3 V.Devices based on Dp An-Bz Ac achieve the highest efficiency,corresponding to the maximum current efficiency,the external quantum efficiency and the power efficiency of the device with the co-host system are 61.8 cd A^-1,17.2%,and 70.0 lm W^-1.More importantly,the efficiency roll-off of the co-host system with m CP has been reduced greatly.We found that the Ph OLEDs with the co-host system of Dp An-Bz Ac and Dp Trz-Bph Bz Ac achieved current efficiency of 57.1 cd A^-1 and 53.0 cd A^-1,with corresponding effciency roll-off of only 7.6%and 0.9%,respectively,from the maximum to the practical brightness of 5000 cd m^-2.Finally,Ip Cm-Ph Bz Ac,Dp An-Bz Ac,and Dp Trz-Bph Bz Ac were used as emitting molecules to study the characteristics of electroluminescence and explore the feasibility using them as emitting molecules.Based on the smaller?E_ST and the high PLQY of Dp Trz-Bph Bz Ac,high-efficiency TADF emission is realized.The maximum current efficiency and the external quantum efficiency of the device with single light-emitting layer with a dopant concentration of 12%Dp Trz-Bph Bz Ac in m CP are 15.19 cd A^-1and 6.63%,respectively.The device with double light-emitting layer based on TCTA and TPBi host exhibit superior performance.The turn-on voltage is 3.4 V,and the maximum current efficiency and the external quantum efficiency are increased to 26.06cd A^-1 and 9.91%,respectively.In addition,the efficiencies of OLEDs devices using Ip Cm-Ph Bz Ac and Dp An-Bz Ac as emitting molecules is low,and need to be further optimized and improved.Through the research of acridine heterocyclic derivative system,this dissertation finds that the novel TADF materials applied in OLEDs exhibits excellent performance and reduces the efficiency roll-off at high luminescence.Therefore,the acridine heterocyclic derivatives have great prospects in the practical application of high-efficiency OLEDs,especially in the field of high-brightness display and lighting.