Study On White Organic Light-emitting Diodes With Non-doped Ultra-thin Emissive Layers Based On Exciton Management

Organic light-emitting diode,which is regarded as the future of display technology,has attracted significant attention as a result of its favorable properties(such as self-emitting,wide viewing angle,low energy consumption,wide color coverage and short response time).Great improvement has been achieved in OLED technology over years and it has now been widely used in consuming electronics.A major focus of OLED research is White OLED since such devices can be used for future full-color display and large-area lighting sources.Non-doped ultra-thin emissive layer is a new novel structure,which is promising for its simple manufacturing process,convenience in optimizing and independence upon host material.However,there is few research on white OLED which adopts this novel structure.This thesis investigates the uneven spatial distribution of excitons in OLED device,and proposes a method which aims to manipulate exction distribution.Finally,we optimized the structure of white OLED based on energy transfer mechanism and exciton management,acquiring a high-performance white OLED device.We first fabricate a series of individual RGB devices to explore the spatial distribution of excitons.As most of host materials we use in OLED are either hole-transporting type or electron-transporting type,and different transporting materials have different charge-carrier conducting abilities,excitons distribute unevenly which could has huge impact on the OLED device.A series of white OLED devices using non-doped ultra-thinemissive layers have been made to demonstrate the influence of the uneven distribution on OLED fabrication.We will see emissive layers which locate far away from the exciton recombination zone cannot be fed with enough excitons to emit,which also has negative effects on device efficiency.Secondly,in order to solve the puzzling problem precipitated by this uneven distribution of excitons,we propose a method which aims to manipulate the distribution of excitons,based on energy level principle.This method is about using a hole-trapping layer whose HOMO energy level is higher then the one of host material,capturing large numbers of holes and hence creating another exciton recombination zone.Finally,we optimize the structure of white OLED with the help of previous works.We get appropriate location of emissive layers by looking into energy transfer mechanism.Also,we optimize the spectrum of white OLED by managing the distribution of excitons and acquire a high-performance white OLED device.