Preparation Of High-efficiency Blue Light-emitting Diode Using Double Exciton Blocking Layer

At present,organic light-emitting diodes(OLEDs)are widely used in flat panel display and solid-state lighting technologies due to their high efficiency,ultra-thin,flexible,wide color gamut,etc.,but how to improve their performance is still the focus of research,especially how to achieve high efficiency and high stability of blue organic light emitting diodes.Compared with blue fluorescent OLEDs and blue thermally delayed fluorescent OLEDs,blue phosphorescent OLEDs have attracted much attention because it can make full use of singlet and triplet excitons to achieve 100% internal quantum efficiency in theory.In this thesis,blue phosphorescent materials FCNIrpic and FIr6 are selected as the light-emitting materials,and materials with higher triplet exciton energy are used as charge transport layers on both sides of the light-emitting layer.Vacuum thermal evaporation technology is used to prepare high-efficiency blue phosphorescence OLEDs,to study the improvement of the performance of blue light emitting devices by the double exciton blocking layer.In addition,in order to understand the interaction between charge and exciton in the process of device luminescence,we also prepared a unipolar hole/electron device and studied its photoluminescence characteristics.The main contents of this paper are as follows:(1)The first chapter mainly introduces the development process and light-emittingmechanism of organic light-emitting diodes and blue OLEDs,systematically analyzes the application value of blue organic light-emitting diodes,and elaborates the research basis and significance of this paper.(2)The second chapter introduces the sample making process and measuring method.It mainly includes the cleaning of substrates,the use of spin coaters,the growth of organic thin films,the packaging of samples,and the measurement methods and processes of electroluminescence and photoluminescence of devices.(3)The third chapter mainly introduces the use of FCNIrpic as a light-emitting material,studies the effect of different doping concentrations of light-emitting materials on the performance of dark blue OLEDs,and obtains the best doping concentration for device performance.At the optimal concentration and other concentrations,NPB,TAPC and TPBi,TmPyPB are used as the charge transport layers on both sides of the light emitting side,respectively.It is experimentally obtained that compared with the dark blue phosphorescent organic light emitting diodes(PhPLEDs)without exciton blocking structure(NPB / mCBP: FCNIrpic / TPBi),the dark blue with dual exciton blocking structure(TAPC / mCBP: FCNIrpic / TmPyPB)PhPLEDs have a lighting voltage of3.5V,a maximum brightness of 23365cd/m2,a maximum current efficiency of 19.4cd/A,and a brightness of 1000cd/m2,and the external quantum efficiency of the device is9.8%.The maximum current efficiency of the device is increased by 4.6 times,and the life of the device is also increased by 3 times.(4)The fourth chapter mainly introduces on the basis of the above devices,using FIr6 as the light-emitting material,to study the degree of improvement of the performance of the clear blue PhOLEDs by the structure of the double exciton barrier layer.Then,by changing the doping concentration and thickness of the light-emitting layer,the performance of the azure blue OLEDs is further optimized,and finally a azure blue phosphorescent organic light emitting diode with a simple and efficient structure is obtained.When the doping concentration of FIr6 is 10%,the thickness of the light-emitting layer is 35 nm,and the driving voltage is 10.5V,the brightness of its clear blue PhOLEDs is 23281cd/m2,the current efficiency is 19.16%,and when the Brightness is 1000cd/A,the external of quantum efficiency is 9.12%.(5)The fifth chapter mainly studies the quenching effect of holes and electron currents on excitons.During the light-emitting process of an organic light emitting diode,there are both an electron current and a hole current,both of which have a quenching effect on the light emitting excitons,but at the same voltage,the electron and hole current have different quenching effects on excitons.Therefore,in this paper,FIr6 is used as a light-emitting material to prepare unipolar holes and unipolar electronic devices.At different voltages,the current densities of unipolar hole devices and unipolar electronic devices are compared,and unipolar holes and monopolar devices are compared.The intensity of the photoluminescence spectrum of the polar electronic device varies with the current density.The degree of quenching of excitons by the holes and electrons flowing in the blue OLEDs during light emission is studied.