Research On Organic Light-emitting Diodes Based On Novel Exciplexes

Exciplexes have attracted enormous attention in the organic light-emitting diode(OLED)field in recent years due to their natural thermally activated delayed fluorescence(TADF)characteristic.Both as TADF emitters or as hosts,remarkable device performance has been achieved.As an indispensable part of forming exciplexes,electron-donating and electron-accepting molecules(Donor and Acceptor)have made great progress in recent years.However,there are relatively few types of Donor and Acceptor reported at present,and the energy level range is narrow.They are commonly used to form yellow-green exciplexes,and there are few reports on red exciplexes,which limits the further development of exciplexes.Therefore,it is of great significance to develop a variety of orange-red exciplexes.To enrich the selection of exciplexes,a series of novel exciplexes have been obtained by using Acceptor with deep LUMO energy level and Donor with shallow HOMO energy level.The OLEDs with emitting orange-red lights and excellent device performance have been successfully fabricated.The specific research contents are as follows:1.It was found that the three Acceptors TRZ-1SO₂,TRZ-2SO_2,and TRZ-3SO₂exhibit deep LUMO energy levels of-3.38,-3.58,and-3.74 eV,respectively.Combining them with 4,4'-bis(carbazole-9-yl)biphenyl(CBP)respectively,novel exciplexes with luminescent color ranging from blue to green was obtained.To further enrich the application of these Acceptors in exciplex-based OLEDs,by using 1,3-bis(9,9-dimethylacridin-10(9H)-yl)benzene(13AB)as the Donor,a series of exciplexes were constructed with the maximum external quantum efficiency(EQE)of more than 5%.And the OLED using 13AB:TRZ-3SO₂ as the emitter exhibits an orange-red emission peaking,which is beneficial to promote the development of exciplexes.Besides,we have fabricated a series of phosphorescent OLEDs(Ph OLEDs)using the interfacial exciplex hosts CBP/Acceptor sensitized red phosphorescent material Ir(MDQ)₂(acac),all of which exhibit a lower turn-on voltage.The maximum external quantum efficiencies of the devices based on TRZ-1SO₂ and TRZ-2SO₂ are 23.1%and 24.4%,which exhibit superior performance compared with the 3,3'-(5'-(3-(pyridin-3-yl)phenyl)-[1,1':3',1''-terphenyl]-3,3''-diyl)dipyridine(TmPYPB)-based contrastive devices.2.It was found that TPA-DMAC,TPA-PXZ,and TPB-PXZ exhibit high HOMO energy levels of-5.4,-5.26,and-5.33 eV,respectively,which had the potential to be used as Donor to form exciplexes.A series of novel exciplexes with various emitting colors were obtained by combining them with PO-T2T,B3PYMPM,and B4PYMPM,respectively.A series of OLEDs have been fabricated based on these novel exciplexes.And the OLEDs using TPA-PXZ:PO-T2T,TPA-PXZ:B3PYMPM,and TPA-PXZ:B4PYMPM as the TADF emitter exhibit low turn-on voltages.Their emission wavelengths are 584 nm,560 nm,and 564 nm,respectively,which exhibits an orange-red emission peaking.The external quantum efficiency is 1.08%,7.64%,and 6.37%respectively.