Regulation Of Electron Injection For Inverted Organic Light Emitting Devices

Organic light-emitting diode(OLED)are regarded as the most competitive next-generation display technology due to their advantages of independent light-emitting,high brightness,high response speed,ultra-thin flexibility and so on.Active driven OLEDs are more widely used.Inverted OLED has become a research hotspot because it can be better integrated into the TFT backplane of the active drive OLED.The low efficiency of electron injection is one of the main problems that plagues inverted OLED,therefore,this article mainly works on the electron injection of OLED with inverted bottom emitting structure,and proposes two feasible solutions to improve the electron injection.The main contents include:(1)Al/Li F electron transport layer was used to modify the electron injection layer Zn O in the inverted device to increase the electron transport capacity of the cathode.The influence of different thickness and evaporation rate of Al film on the inverted OLED device was investigated.The experimental results show that Al at lower evaporation rate can better act as the role of hole blocking.When the evaporation rate is 1 Hz/s and the thickness of Al is 2nm,the device performance is the best,and the maximum current efficiency of the device is increased from 0.49 cd/A to 4.21 cd /A without modification of Zn O device.(2)Zn O nanoparticles were used as the cathode injection layer of the inverted OLED,and an amino acid,D-arginine,was used to modify the surface of Zn O.By comparing the different membrane forming modes of D-arginine,the self-assembly membrane forming mode with better performance was selected.The three factors affecting the self-assembly film formation were investigated: the concentration of D-arginine,soaking time and lifting speed.It was determined that the device performance reached the best when the concentration of D-arginine was 1 mg/ m L,soaking time was 2 h and the lifting speed was 5mm/min.At the same time,compared with the polymer electrolyte PEI reported in the literature,the results show that the light starting voltage of the device based on the amino acid modification decreases by 0.3V compared with that of the device modified by PEI.The current efficiency of the device increases from 4.13 Cd /A to 4.58Cd/A.(3)Two kinds of heterojunctions with P-N junction structure are proposed as cathode injection layers for inverted OLED,which can effectively enhance cathode electron injection.The first heterojunction is Ni Ox/Zn O,which has a higher electron injection capability than the Zn O injection layer which relies on ITO electrode injection by single electron device characterization.Compared with the structure without heterojunction,the device efficiency increases from 4.1cd /A to 5.2cd /A,and there is no current efficiency attenuation at high voltage.The second heterojunction is PEDOT:PSS/Zn O,and the device performance is slightly improved after adding this heterojunction.