Tetradentate Pt(Ⅱ)complex as a singlet exciton sensitizing host for highly efficient green fluorescent organic light-emitting diodes

Efficient green fluorescent organic light-emitting diodes were designed with a phosphorescent metal complex as a singlet exciton sensitizing host(SESH)for achieving high efficiency and low efficiency roll-off through exciton and polaron management.Tetradentate Pt(Ⅱ)complex(Pt-Trz)possessing a tetradentate ligand with a bulky blocking group not only suppresses the severe formation of excimer or dimer itself but also transfers radiative excitons to fluorescent dopant effectively.The SESH assisted fluorescence(SESHF)device with Pt-Trz as the host exhibits the maximum external quantum efficiency of 13.3%and a lower efficiency roll-off compared with exciplex host device which is a general approach for harvesting triplet excitons.Numerical exciton dynamics modeling unravels that the SESHF device effectively utilizes triplet excitons in the host by intersystem crossing and resonance energy transfer from the triplet state of the host to the singlet state of the terminal emitter.Bimolecular quenching rates of the SESHF device are reduced by 11 times for triplet-triplet annihilation and 1.8 times for tripletpolaron annihilation compared with the exciplex device,which demonstrates that Pt-Trz could be a platform to be used as an efficient host for fluorophores.

A silane-based host material with improved electron transport properties for phosphorescent OLEDs with high efficiency and low efficiency roll-off

A dibenzosilole-based host material was designed and characterized.The host material,9,9'-(5,5-diphenyl-5H-dibenzo[b,d]silole-2,8-diyl)bis(9H-carbazole)(SSiCz),was designed to enhance the electron transport properties and rigidity by coupling two phenyl units of the tetraphenyl silane of a strong hole transport type bis(4-(9Hcarbazol-9-yl)phenyl)diphenylsilane host.The device efficiency roll-off was improved considerably by balancing the carriers in the phosphorescent organic light-emitting diodes(PhOLEDs),and the driving voltage at high luminance was reduced.The red and green PhOLEDs exhibited high external quantum efficiencies(EQEs)of 23.8%and 24.9%,respectively,and a relieved efficiency roll-off.In addition,S-SiCz was used as an electron transport type host with a hole transport type3,3'-di(9H-carbazol-9-yl)-1,1'-biphenyl host.The maximum EQEs of the red and green PhOLEDs using the mixed host were 26.0%and 25.5%,respectively,and EQE roll-off values were 18%and 6%,respectively.Therefore,the planarization design strategy of the host is effective for better device performance.

Indolo[3,2,1-jk]carbazole-derived planar electron transport materials realizing high efficiency in green phosphorescent organic light-emitting diodes

Two novel electron transporting materials(ETMs),2-(4,6-diphenyl-1,3,5-triazin-2-yl)indolo[3,2,1-jk]-carbazole(DPTrz-ICz)and 5,11-bis(4,6-diphenyl-1,3,5-triazin-2-yl)-2-phenylindolo[3,2,1-jk]carbazole(2DPTrz-ICz),were developed based on the indolo[3,2,1-jk]carbazole(ICz)core,combined with 2,4-diphenyl-1,3,5-triazine(DPTrz).The introduced ICz core in ETM exhibited enhanced intermolecular charge transport properties owing to its planar and rigid geometry and high triplet energy,demonstrating the potential of designing ETM.Consequently,2DPTrz-ICz,featuring high triplet energy of 2.84 eV,effectively prevented triplet exciton quenching and showed increased electron mobility owing to the activation of intermolecular hopping charge transfer facilitated by stacking architecture.The two materials were utilized as ETMs in green phosphorescent organic light-emitting diodes.2DPTrz-ICz exhibited a superior external quantum efficiency of 21.5%,higher than that of the spirobifluorene-derived ETM.

A novel benzo[4,5]furo[3,2-d]pyrimidine-based host as a n-type host for blue phosphorescent organic light-emitting diodes

An electron-transport-type host was synthesized using a benzo[4,5]furo[3,2-d]pyrimidine(BFP)core to develop a high triplet energy host.The host was designed to have both the tetraphenylsilyl blocking group and the hole-transport-type carbazole group.In the device application,the host was used as an electron-transport-type host mixed with a hole-transport-type 3,3'-di(9H-carbazol-9-yl)-1,1†-biphenyl(mCBP)host in the blue phosphorescent organic light-emitting diodes(PhO-LEDs)doped with a[[5-(1,1-dimethylethyl)-3-phenyl-1H-imidazo[4,5-b]pyrazin-1-yl-2(3H)-ylidene]-1,2-phenylene]bis-[[6-(1,1-dimethylethyl)-3-phenyl-1H-imidazo[4,5-b]pyrazin-1-yl-2(3H)-ylidene]-1,2-phenylene]iridium(Ir(cb)3)blue phosphor.As a result,the mCBP:CzBFPmSi mixed host showed high external quantum efficiency over 20%at 1000 cd m^(−2) and low efficiency roll-off in the blue PhOLEDs.