| After being discovered by Prof.Ching.W.Tang in the 1980s,Organic Light-Emitting Diodes(OLEDs)have been developed for several decades with the advantages of lightness and thinness,wide visual angle,flexibility,wide color gamut,energy saving and so on.Now they have gradually entered people's life and become a new generation of light-emitting devices for display and lighting.The current OLED light-emitting materials are mainly divided into traditional fluorescent,phosphorescent and thermally activated delayed fluorescent materials.Meanwhile,through the appropriate selection of donors and acceptors and the up-conversion of triplet,exciplex,the thermally activated delayed fluorescent materials based on intermolecular charge transfer,can achieve theoretical 100%excitons harvesting efficiency and can also markedly reduce the efficiency roll-off with a wider excitons recommendation region.Therefore,they raised tremendous attention from researchers concerning their applications as emitters and hosts.However,to date,there are more studies on monochromic light-emitting exciplexes,while there are relatively few white OLEDs(WOLEDs)based on pure light-emitting exciplexes.For the application as hosts,in addition to the sensitization of fluorescent,phosphorescent and other light-emitting materials,it is also necessary to expand their application range as the hosts and explore their universal characteristics as the hosts.In this thesis,focused on the exciplex,the applications as emitters and hosts of exciplex based on triplet exciton up-conversion in the OLEDs were studied.Specific research contents are as follows:1.Based on the wide spectral coverage of the exciplex,we used the blue mCP:POT2T exciplex and the orange TAPC:POT2T exciplex as the emitting layer,respectively,to prepare the WOLEDs with pure exciplex and complementary colors.Through the using of DPEPO interval layers and changing the number and position of them,high color stability and high color rendering index(CRI?80)complementary color WOLEDs were finally achieved.Current efficiency,power efficiency and external quantum efficiency reached 16.2 cd/A,11.3 lm/W and 7.92%,respectively.When operating voltage rised from 6 V to 9 V,the CIE coordinates only changed with(±0.00,±0.02).This study shows that the exciplexes hold a great potential as emitters in realizing high CRI WOLEDs.2.The blue mCP:POT2T exciplex as the host,and the red fluorescent material DCJTB as the guest were used to prepare the WOLEDs with high efficiency and low efficiency roll-off.When the guest reached the optimal doping concentration of 0.6 wt%,current efficiency,power efficiency and external quantum efficiency of WOLEDs reached 17.4 cd/A,13.7 lm/W and7.60%,respectively.The device achieved highly efficient emission that exceeded the limit of 5%of the external quantum efficiency of the fluorescent OLEDs and the decay of external quantum efficiency from maximum to that at1000 cd/m2 was only 17.4%.It is shown that utilizing exciplexes as hosts can enhance the efficiency of fluorescent devices and improve the efficiency roll-off.3.Utilizing the exciplex formed by donor TCTA and acceptor Bphen as the host and rare earth complex Eu(DBM)3Phen as the guest,red OLEDs with low turn-on voltage and low efficiency roll-off were prepared.The device obtained the turn-on voltage of 2.9 V,the external quantum efficiency of 2.12%,and the efficiency roll-off of external quantum efficiency from the maximum to that at100 cd/m2 was only 12%.Futhermore,OLEDs were replaced with host from TCTA:Bphen exciplex to mCP:POT2T exciplex and achieved a higher external quantum efficiency of 3.11%.It is demonstrated that the exciplexes can not only be used as the hosts of traditional fluorescent and phosphorescent materials,but can also be used as the hosts of rare earth complexes,expanding the application range of exciplex hosts. |
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