Synthesis Of Bipolar Host Materials And Study On OLEDs Devices

Organic light-emitting devices (OLEDs) are a new type of light-emitting devices which hasincomparable advantages with traditional display devices. It has preferable application prospectin the field of displays and solid-state lighting. OLEDs have many distinctive features, such asself emission, fast response, thin thickness, flexible, lower production costs and so on. Despitethe realization of OLED commercialization in displays of both small and large size, the OLEDsstudies focusing on higher efficiency and more cost effective, as well as further improvingdevice lifetime are still the hot research topics in OLEDs.This article focuses on synthesis of bipolar hosts, device physics, heat revolution on OLEDdevices and interface optimization, which mainly includes four aspects as follows:Firstly, two structurally similar host materials based on carbazole moiety were synthesizedfor phosphorescent OLEDs. By structural characterization of high resolution mass spectrometer,1H-NMR, and elemental analyses, it ascertained that molecular structures of the two newsynthesized materials were correct.Secondly, we studied the photophysical, electrochemical, thermal properties of the two newsynthesized materials. By parallel study it was demonstrated that introduction of inert tert-butylgroup has a slight influence to the photophysical and electrochemical properties of materials butimproved material thermal stability. Then, based on the two materials, we fabricatedphosphorescent organic light-emitting devices (PhOLEDs) with analogous structure, and foundthat the introduction of tert-butyl has little effect on the freshly prepared OLED devices.Thirdly, we studied the effects of heat revolution on both material properties and relatedOLED devices. It was found that performance of tBu-o-CzOXD:Ir(ppy)3based OLEDs showedan82.2%increase when the device was heating to90oC for10minutes in air.Lastly, we introduced anode modification in our devices. Since OLEDs are double injectiondevices that electrons and holes are injected to emitting layer from cathode and anode,respectively, the balance of charge carriers injection is key to achieve high performance.Therefore, reduction of injection barrier and balance carrier density of emitting layer is aneffective method to improve the performance of OLEDs. We found that inserting hole injectionlayer (EIL) PEDOT:PSS can improve device efficiency. Additionally, some organic solventswere introduced. By spin-coating several drops of ethanol, acetone and N,N-Dimethylformamide (DMF) on top of the PEDOT:PSS film, positive effect on device performance was demonstrated.The current efficiency of standard device is increased by as large as70%after DMF treatment.While adding PEDOT:PSS to the phosphorescent devices, the efficiency was twice higher thanthe device without anode modification.