Effects Of Dilution Concentration And Multi-component System On The Optical-electrical Performance Of Exciplex

Organic light-emitting diodes(OLED)have been widely used in solid-state lighting,flat displays and flexible screens because of the advantages of self-emitting,wide color gamut,high contrast and flexible.The emitters of OLED are mainly divided into traditional fluorescent,phosphorescent and thermally activated delayed fluorescent(TADF)materials.Among them,the TADF emitter based on intramolecular charge transfer is more difficult to achieve small single triplet energy gap(ΔEST).While,exciplexes based on intermolecular charge transfer have attracted much attention for easily acquired smaller ΔEST by selecting appropriate donors and acceptors.Theoretically,100% exciton utilization can be achieved in exciplex.Here,we focus on exciplex to study the effect of donor/acceptor ratio and multi-mixed system on device performance.Finally the pure red exciplex is explored by multi-donor/acceptor component system.The research contents of this thesis are as follows:1.High-efficiency exciplex OLED are obtained by diluting the exciplex concentration through constructing different ratios of donors and acceptors.A green exciplex of DMAC-DPS:PO-T2 T was formed by using TADF donor of 10,10′-(4,4′-Sulfonylbis(4,1-phenylene))bis(9,9-dimethyl-9,10-dihydroacridine(DMAC-DPS)and conventional acceptor of 2,4,6-Tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine(PO-T2T).The exciplex concentration was then diluted using two methods: The first method is to change the weight ratio of acceptors,when the content of PO-T2 T is controlled at 0.5 wt%,the external quantum efficiency of the device is 10.8% and its electroluminescent spectrum blue-shifts to 488 nm.Another is to add the inert host material of Bis[2-(diphenylphosphino)phenyl]ether oxide(DPEPO)to dilute the exciplex concentration under the condition of donors/acceptors ratio at1:1.When the DPEPO concentration reaches 70 wt%,the OLED with the highest external quantum efficiency of 9.4% is obtained,and the electroluminescent spectrum is blue-shifts to508 nm.Both of two dilution methods can change the exciton energy,achieve spectral blue shift,reduce exciton quenching,and thereby improve device efficiency.2.Construction of a ternary exciplex system with multiple reverse intersystem crossing(RISC)processes.Different polar donor materials 1,3-Di(9H-carbazol-9-yl)benzene(m CP),DMAC-DPS and PO-T2 T were blended in the emitting layer.The effect of different polar materials on the optoelectronic properties of the device was explored by fixing to donor/acceptor ratios of DMAC-DPS:PO-T2T(1:1)and m CP:PO-T2T(1:1)and changing the doping weight ratio of m CP and DMAC-DPS,respectively.When the m CP concentration of70 wt% in DMAC-DPS:PO-T2T(1:1)layer,the maximum external quantum efficiency reach to 13.4%.At the same time,the devices have a low efficiency roll-off with the electroluminescent spectrum blue-shifts to 504 nm.It was found that different polar materials have different effects on the energy transfer process of exciplexes.Bipolar materials can maintain the stability of the device as well,and the device can still maintain a very low efficiency roll-off at high voltage.There are multiple exciplexes or materials with TADF effect in the multi-system.The multi-RISC processes could optimize the energy transfer pathway and improve the exciton utilization rate.At the same time,the multiple exciplexes could obtain high-efficiency by diluting with each other to reduce the quenching of exciton concentration.3.The red all exciplex device was fabricated by multi-component system.The multi-component system has an obvious effect on the external quantum efficiency,so it is an effective way to apply this idea to red exciplex.The blue-shift of the spectrum of m-MTDATA:PO-T2 T exciplexes was realized,and more efficient red exciplexes were obtained by incorporating 4,4’,4’’-Tris[(3-methylphenyl)phenylamino] triphenylamine(m-MTDATA)into exciplexes with different donors and PO-T2 T.At the same time,the effects of different polar donor materials on red exciplex were explored.The TADF material of DMAC-DPS which used as a donor to form exciplex host of DMAC-DPS:PO-T2 T,exhibit an obvious optimization effect.When the m-MTDATA concentration of 20 wt% in DMAC-DPS:PO-T2T(1:1)layer,a red emission with a peak of 628 nm was obtained with CIE coordinates at(0.56,0.43).Compared with the m-MTDATA:PO-T2 T exciplex,the device efficiency is also improved greatly.The exciplex system utilizes multi-component donor/acceptor,improves the utilization rate of excitons,optimizes the energy transfer pathway,and achieves better performance...