Study On Structure Optimization And Emitting Characteristics Of OLED Devices Based On Exciplex Host

In order to obtain high-performance OLED devices,many researchers choose thermally activated delayed fluorescence(TADF)materials to prepare devices,but the design process of TADF materials has very strict requirements for molecular structure,the exciplex,on the other hand,provide the same results as conventional TADF materials in a much simpler way.This thesis focuses on the effects of exciplex on device performance and emission mechanisms.The performance of the exciplex devices is enhanced by optimizing the guest doping,selecting a suitable exciplex host and an ultrathin emitting layer under the interfacial exciplex in order to optimize the emission mechanism,charge transfer capability and the emission center of the emitting layer.The specific study is divided into three parts:Firstly,CBP was used as the electron donor for the host of exciplex,B3Py MPM was used as the electron acceptor for the host of exciplex,and green phosphorescent material fac-Ir(ppy)₃ as the guest.OLED devices with doping concentrations ranging from low to high for the host of exciplex were prepared.At a doping concentration of 7 wt%,the devices with current efficiency(CE),power efficiency(PE),and external quantum efficiency(EQE)of 82.43 cd/A,86.32 lw/W,and 24.43%,respectively.The electroluminescence spectra were analyzed to reveal the relationship between the doping concentration variation and the emission mechanism.Then,five the host of exciplex devices were prepared on the basis of determining the optimal doping ratio of fac-Ir(ppy)₃ by 7 wt%.And the devices with the maximum PE of 87.21 lm/W and the maximum EQE of 25.12%were obtained at the m CP:B4Py MPM host.It was revealed that the reason for the high performance of the m CP:B4Py MPM host devices was due to the excellent device structure and the optimization of the emission center.Finally,CBP was used as the electron donor of the interfacial exciplex,B3Py MPM was used as the electron acceptor of the interfacial exciplex,and fac-Ir(ppy)₃ as the ultrathin light-emitting layer.Five sets of interfacial exciplex devices with different thicknesses of ultrathin light-emitting layers were prepared.When the ultrathin emitting layer was 0.2 nm,the devices obtained maximum CE,PE,EQE of 65.55 cd/A,68.64lm/W,18.72%,respectively.The electroluminescence spectra reveal that the best performance obtained at 0.2 nm is due to the suitable thickness and the more excellent emission mechanism.