Development And Optimization Of Top-emitting Organic Light-emitting Diodes

With the development of materials science and device physics,Active-Matrix Organic Light-Emitting Diode(AMOLED)technology has gradually matured,and more and more applications in the field of consumer-grade displays and lighting.With the development of VR/AR,silicon-based microdisplays based on AMOLED have also become the focus of attention in the industry.Since AMOLEDs require technical characteristics of high aperture ratio,high luminance,and high color purity,top-emitting OLEDs structures were widely used in AMOLED panels and OLED microdisplay devices.Although the theoretical research on top-emitting OLEDs has been deepened,there were still optimization space for the fabrication cost and device efficiency of top-emitting OLEDs under the requirements of OLED industrialization.For this reason,the anode,cathode,capping layer and microcavity weakening of the top-emitting OLEDs were studied.The main work contents are as follows:(1)The effects of Ag and Al metal anodes and Ag/Al,Ag/Au and Al/Au composite anode structures on the performance of top-emitting OLEDs devices were investigated.Ag/Au anode shown best performance.A high-efficiency top-emitting OLEDs device based on Ag/Au composite anode and Ir(ppy)3 double-emitting layer was prepared during the experiment.The turn on voltage was about 2.7 V,and the maximum current efficiency was up to 73.4 cd/A.It has a high brightness of 6473 cd/m2 at 10 mA/cm2,and a narrow FWHM of 32 nm,meanwhile,the color coordinate(CIE1931)was(0.17,0.70),and the roll-off at 6473 cd/m2 was only 12%.The effect of different evaporation rates of Al anodes on the performance of top emitting OLED were also studied.It was found that the rate of 5 A/s was a better evaporation rate,while the too low rate affects the injection effect of the anode.In addition,an array structure was fabricated by laser etching.We compare the performance by preparing the devices.The devices have a best performance when the sides of the squares that make up the array was 40?m.The highest brightness and the highest current efficiency reached 19955 cd/m2 and 66.7 cd/A,which was 10.4%higher than that of the non-array structure device.This kind of structure was simple and reliable,and its pattern change was easy and low cost,so it was easy to industrialize.(2)An experimental study was carried out on the influence of the thickness of Ag cathode on the microcavity of the top-emitting OLED device.It was found that the increase of the thickness of the transparent electrode could effectively narrow the luminescence spectrum of the device and improve the color purity of the device.However,at the same time,a thick Ag cathode will lead to a decrease in transmittance and the light extraction efficiency of the device.In addition,using the content studied in this section,a large area of microcavity-based deep red OLED light was manufactured.The OLED light has a high external quantum efficiency of 20.1%,and the color coordinates(CIE1976)was(0.55,0.52).In the study of capping layer,TCTA was used as the capping layer of Ir(ppy)3-based green phosphorescent top-emitting OLED device,and the effect of its thickness on device efficiency and spectrum was studied.It was found that different thickness of capping layer can extract the light of different wavelengths.In addition,four different structures of TCTA(40 nm),CBP(40 nm),TCTA(20 nm)/CBP(20 nm)and CBP(20 nm)/TCTA(20 nm)were compared.The device with TCTA capping layer was the most efficient,the device with CBP as the overlay was the least efficient,and the device with the composite structure capping layer had the efficiency between the two single capping layer devices,and the two devices with the composite structure capping layer had the same efficiency.(3)The color-angle dependence in top emitting OLED was studied,and the scattering structure of the anode substrate was fabricated by nano imprinting.The nano-imprinted anode substrate greatly weakened the microcavity effect and reduced the color-angle dependence of the top-emitting OLED device,when the viewing angle was changed from 0° to 45°,the spectral peak position was only shifted by 1 nm.