Font Size: a A A

Synthesis Of Novel Emitters Based On Thermally Activated Delayed Fluorescence And Their Applications On Organic Light-emitting Diodes

Posted on:2020-10-29Degree:MasterType:Thesis
Country:ChinaCandidate:J L CaiFull Text:PDF
GTID:2428330596476477Subject:Engineering
Abstract/Summary:PDF Full Text Request
Thermally activated delayed fluorescence?TADF?emitters have attracted great attention from academia and industry due to their superior performance in organic light-emitting devices?OLEDs?.With the small singlet-triplet energy gap,triplet excitons can be upconverted to singlet excitons by reverse intersystem crossing.Therefore,TADF OLEDs can achieve 100%internal quantum efficiency theoretically.A large number of green TADF emitters have achieved high efficiency in OLEDs.However,the high-efficiency TADF materials in the other wavelength are still scarce.In this paper,high efficiency blue and yellow TADF emitters are designed and synthesized for this problem,and the following results have been achieved.1.In order to obtain a high efficiency TADF emitter with a shorter wavelength band,a novelTADFemitter2,4-diphenyl-6-?4-?1,3,6,8-Tetramethyl-?carbazol-9-yl?phenyl)nicotinonitrile?tMCzPN?wasdevelopedbyusing1,3,6,8-tetramethylcarbazole as an electron donor and triphenylnicotinonitrile as an electron acceptor.The extra steric hindrance induced by the methyl group resulting in a highly distorted molecular structure,tMCzPN achieves better separation between the highest molecular orbital?HOMO?and lowest molecular orbital?LUMO?.The HOMO and LUMO energy levels of tMCzPN were estimated to be-5.66 and-3.13 eV,respectively.In the DPEPO-doped film,the fluorescence peak of tMCzPN is 487 nm,and the peak of phosphorescence is 507 nm;the single-triplet energy gap of 0.10 eV ensures the TADF characteristics of tMCzPN.In OLED devices,tMCzPN successfully exhibits blue emission with CIE coordinates of?0.20,0.42?,and achieves extremely high device efficiency without any light output coupling enhancement,among which maximum current efficiency,power efficiency and external quantum efficiency were 65.9 cd A-1,62.7 lm W-1 and 26.0%,respectively.These results indicate that tMCzPN is a highly efficient blue TADF emitter.2.In order to obtain a longer wavelength high efficiency TADF emitter,a compound1,4-bis?5-?phenoxazin-10-yl?pyrimidin-2-yl?benzene?pPBPXZ?was designed and synthesized using phenoxazine as electron donor and pyrimidine as electron acceptors.Due to the large steric hindrance of phenoxazine,pPBPXZ achieves a highly distorted molecular structure,which allows a good separation between HOMO and LUMO.pPBPXZ exhibits a small singlet-triplet energy gap of 0.09 eV.The wavelength peak of pPBPXZ in the toluene solution is 535 nm.An OLED device using pPBPXZ as emitter successfully achieved yellow emission with a peak of 556 nm and CIE coordinate of?0.41,0.56?,and achieved a maximum external quantum efficiency of 15.7%without any light output coupling enhancement.These results indicate that pPBPXZ is a superior yellow TADF emitter.
Keywords/Search Tags:organic light-emitting devices (OLEDs), thermally activated delayed fluorescence(TADF), carbazole, pyrimidine
PDF Full Text Request
Related items