Fabrication And Photoelectric Properties Study Of Organic Light-emitting Diode With Different Electron-transport Materials

In the 21 st century,new-generation flat panel displays with better performance are needed to meet the requirements of the "4C"(communications,automotive electronics,computers,consumer electronics)and "4G"(fourth mobile communication).The organic light-emitting diode(OLED)as a next generation display technology enjoys many advantages over LCD flat panel displays,including self-luminous,wide viewing angle(up to 175?),flexible display,short reaction time,ultra-thin design(less than 1mm),and low operating voltage(3-10 V.Therefore,OLED-based full-color displays are increasingly attractive.However,the OLED technology is far from mature and further improvement of the device performance,manufacturing process and operational lifetime as well as reduction in the production costs are needed.In particular,to achieve broader commercial applications,it is necessary to obtain a greater understanding of the aging mechanisms and further improve the device lifetime.In this thesis,organic devices based on four typesof electron transport materials,Alq3,TPBi,Bphen and TAZ,were fabricated,and their aging begaviors under high current stressing were investigated in order to investigate the impact of electron transporting materials on the luminous efficiency and lifetime of the OLED devices.The main tasks are summarized below:First,in order to determine the intrinsic stability of these four types of electron transport materials(Alq3,TPBi,Bphen,TAZ),electron-only devices were fabricated and characterized(ITO/LiF(1 nm)/ETL(60 nm)/LiF(0.5 nm)/Al(120 nm)).Stress testing showed that Bphen?Alq3>TPBi>TAZ in terms of material stability.Second,Green OLED comprising these four types of electronic transport materials were fabricated through vacuum vapor depsotion(ITO/NPB(50 nm)/Alq3(30 nm)/ETL(30 nm)/LiF(0.5 nm)/Al(120 nm)).Detailed optoelectronic characterization led to identification of three key material factors affecting the OLED lifetime: energy-level alignment between electron transport material and the cathode,the electron mobility and the stability of the material.Due to the highest mobility of Bphen,the LUMO level matched to the Al Fermi level,and the excellent stability,the use of the Bphen electron transport layer resulted in lifetime improvement of the OLED by several times.Finally,we prepared intermixed electron-transport layers through co-evaporation of Bphen and TAZ.The influence of this mixed electron-transport material on the luminance and lifetime of green OLEDs were studied.