Research On Preparation And Properties Of Organic Light Emitting Devices Based On Exciplex

White organic light-emitting devices?WOLEDs?has attracted extensive attention due to its advantages of self-illumination,high efficiency,flat emission and flexibility,and is considered as the ideal next-generation lighting source.Now the efficient usage of exciplex is a hot topic in this field.The efficiency could be improved by using triplet energy of exciton through exciplex,however,there are still some problems to be solved,such as poor color purity and stability of devices,and short lifetime of blue phosphor materials,high production cost of complex structure and low luminous efficiency of traditional fluorescent materials.In this work,by designing a new host-guest structure,dual emission layer fluorescence-phosphorescence hybrid complementary color WOLED was fabricated,high color rendering index?CRI?and high luminous efficiency were realized simultaneously.By utilizing ternary exciplex as the host of yellow thermally activated delayed fluorescence?TADF?materials,the novel energy transfer strategy was achieved and the high efficiency all fluorescence WOLED was obtained.The specific research contents are as follows:?1?The electron transport materials?1,3,5-Triazine-2,4,6-triyl?tris?benzene-3,1-diyl?tris?diphenylphosphineoxide??PO-T2T?was selected to form blue and yellow exciplex with hole transport materials N,N?-dicarbazolyl-3,5-benzene?mCP?and di-[4-?N,N-ditolylamino?-phenyl]cyclohexane?TAPC?respectively.The blue and yellow exciplex were chosen as the host of iridium?III?bis[?4,6-difluorophenyl?-pyridinato-N,C2?]picolinate?FIrpic?and Bis?2-methyldibenzo[f,h]quinoxaline??acetylacetonate?iridium?III??Ir?MDQ?₂acac?respectively to form dual emission layer fluorescence-phosphorescence hybrid WOLED.The devices obtained maximum power efficiency of 73.2 lm/W,maximum current efficiency of 72.2 cd/A,maximum external quantum efficiency of 23.5%.The optimized CRI is 82,and exhibit superior stability with voltage changing.The utilization rate of exciton is improved due to the doping of phosphor materials,and the energy loss in the energy transfer process is reduced due to the small energy difference between the host materials and the guest materials,which improves the efficiency of the device.?2?The electron transport materials PO-T2T,hole transport materials mCP and blue TADF materials bis[4-?9,9dimethyl-9,10-dihydroacridine?phenyl]sulfone?DMAC-DPS?were selected to form a bluish-green ternary exciplex,and as the host of yellow TADF materials 3,4,5,6-tetrakis?3,6-diphenylcarbazol-9-yl?-1,2-dicyanobenzene?4CzPNPh?to form all fluorescence WOLED.The energy gap between singlet and triplet exciton is small enough to achieve high reverse intersystem crossing?RISC?efficiency,and the introduced novel strategy with stepped reverse intersystem crossing channels enhanced the RISC efficiency further.The utilization of exciton was improved efficiently by convert triplet exciton into singlet,which reduced the accumulation of triplet exciton and suppressed the efficiency roll-off.The maximum power efficiency,current efficiency and external quantum efficiency of the device reached to 62.5 lm/W,57.8 cd/A and 22.7%,respectively.The external quantum efficiency kept at 21.4%for the luminance of 1000 cd/m².In summary,based on the deep development and utilization of traditional materials,a high-efficiency all fluorescence WOLED based on ternary exciplex was achieved.The energy transfer mechanism and the influence of the efficiency of RISC on the device efficiency have been analyzed.Based on the binary exciplex as the host,fluorescence-phosphorescence hybrid WOLED was achieved,the luminescence mechanism and the influence of inter-layer on CRI were compared and analyzed.It provides a reference for the design of host and guest system,device structure and energy transfer mechanism of high-performance WOLED devices,and lays a foundation for promoting the commercialization of WOLED in lighting and display fields.