Study On High-efficiency Orange And White Oleds Based On The Energy Transfer Of MCP And PO-T2T Blue Exciplex

In recent years,exciplex has been found to have TADF(thermally activated delayed fluorescence)properties,so the theoretical luminous efficiency of exciplex can reach 100%.Therefore,exciplex has received extensive attention in recent years.In the device structure,exciplex-based light-emitting device structures are generally composed of a donor-acceptor interface structure and a donor-acceptor mixed structure because exciplex-based compounds require sufficient contact between the donor and acceptor materials.The first exciplex phenomenon was found in the interaction between the carrier transport layer and the light-emitting layer of the layered device.This exciplex phenomenon produces exciton emission peaks that are different from that of the light-emitting material and thus interfer monochromatic light,therefore,at that time,people always avoid exciplex emission,but exciplex light-emitting devices based on interfacial structure can also obtain higher external quantum efficiency since the exciplex was found to have TADF properties.Compared with donor-acceptor-mixed exciplex-based light-emitting devices,the exciplex formed by the interfacial structure is limited to the interface between the donor and the acceptor because of the contact area,therefore,the electron and hole transport layers are required to regulate the carrier well.Exciplex light emitting devices with mixed donor and acceptor have more adjustment space.Since the carrier balance of the mixed layer can be regulated by adjusting the mixing ratio of the donor and acceptor,the mixed layer device structure can often achieve higher device efficiency and smaller efficiency roll-off.In this paper,different device structures are designed based on the blue-exciplex formed by m CP and PO-T2 T to achieve orange and white light devices.The main work of this thesis are as follows:1.Formation of an interface between m CP and PO-T2 T.Blue exciplex doped with phosphorescent material Ir(pq)2acac in acceptor PO-T2 T achieves high-efficiency orange emission by controlling the concentration of dopant Ir(pq)2acac.Obtain the best device performance at a doping concentration of 4 wt%.The maximum current efficiency,power efficiency,and external quantum efficiency are 28.75 cd/A,30.10 lm/W,14.98% respectively.Next we adopt two approaches to prepare white-light devices.One is to reduce the doping concentration of Ir(pq)2acac in the acceptor material PO-T2 T to achieve incomplete energy transfer,white-light organic electroluminescent devices.When the doping concentration is 0.3 wt% by weight,we obtained good white light devices with maximum current efficiency,power efficiency and external quantum efficiency of 27.84cd/A,29.15lm/W and 13.57%,respectively.Second,we use the acceptor material PO-T2 T as the spacer layer in the orange light device to achieve the optimal white light organic electroluminescent device by controlling the thickness of the spacer layer.When we obtain the maximum efficiency of the device when the spacer layer thickness is 4 nm The current efficiency,power efficiency and external quantum efficiency were 20.36 cd/A,21.32 lm/W and 10.71%,respectively.2.The use of m CP and PO-T2 T to form a mixed blue-light exciplex achieves an optimal orange-color organic electroluminescent device by doping the phosph-orescent material Ir(pq)2acac in a mixed-exciplex by adjusting the concentration of the dopant.When the doping concentration was 1.5 wt%,we obtained the best device performance and its maximum current efficiency,power efficiency and external quantum efficiency reached 35.3 cd/A,31.0 lm/W,and 18.7%,respectively.Next,we reduced the doping concentration of the dopant Ir(pq)2acac to achieve incomplete energy transfer white light device structure.When the dopant concentration was 0.1 wt%,we obtained a white light device with better performance and maximum current efficiency,power efficiency,and external quantum efficiency reached 15.55 cd/A,13.69 lm/W and 7.49%,respectively,and the efficiency roll-off of orange-and white-light organic electroluminescent devices was significantly improved compared with those of aboved prepared devices based on interfacial structure exciplex.3.We use m CP and PO-T2 T to form a mixed blue-light exciplex as a blue light-emitting layer and ultra-thin layers Ir(ppy)3 and Ir(pq)2acac as a green light-emitting layer and an orange light-emitting layer,respectively.We designed the white organic electroluminescent devices in the order of blue,green,orange and blue,orange and green,respectively.Through a series of optimization measures,the maximum current efficiency,power efficiency and external quantum efficiency of white organic electroluminescent devices based on blue,green,and orange sequences reached 24.06 cd/A,21.59 lm/W and 10.24%,respectively.The maximum current efficiency,power efficiency and external quantum efficiency of organic EL devices in the order of blue,orange and green reached 38.83 cd/A,34.85 lm/W and 15.28%,respectively.