Reasearch On Red Organic Light-emitting Devices Based On NiO_x Surface Modification And Double-emissive Layers

Organic light-emitting devices?OLEDs?have attracted extensive attention in the academic and industrial field over the past two decades due to their potential applications in flat panel displays and solid-state lighting.In particular,the introduction of phosphorescent triplet light-emitting materials in OLEDs has made great breakthroughs in improving electroluminescent efficiency.At the same time,it has also accelerated the speed of bringing OLED products to the market,providing a feasible solution for the commercialization of the large-scale OLED industry.However,red phosphorescent materials have a narrow emission band gap and severe exciton quenching.Compared with green OLEDs,there is a large gap in light emission efficiency.The research and development of high-efficiency red OLED devices is very important to improve the yield of OLED products,improve the luminous efficiency of devices,and reduce the production costs of OLED product lines.This article is based on NiOx surface modification and the use of a double light-emitting layers structure to improve the performance of red OLED devices.1.We used nickel oxide?NiO_x?synthesized by the sol-gel method as the hole injection layer for OLED devices.O₂-plasma treatment of the NiO_x surface increased the work function of the NiO_x film,and the hole injection barrier at the NiO_x/TAPC interface decreased,which increased the hole concentration of NiO_x and improved the conductivity of NiO_x film,Leading to increased current density of the device and improved performance of the red OLED device.A red OLED device which used NiO_x treated with O₂-plasma as the hole injection layer achieved a current efficiency of 5.2 cd/A and an external quantum efficiency of 7%,which was 1.75 times and 1.73 times higher than the original device,respectively.Solution-processing for hole injection layer of OLEDs can reduce manufacturing cost and realize application on large area devices and flexible substrates.2.We designed an OLED device with a double-emissive layers structurewhich used different conductive type host materials.The host material of the first emissive layer was CBP which was one of hole-transporting materials and the host material of the second emissive layer was TPBi which was one of electron-transporting materials,which improves the carrier balance of the red OLED device and increased the utilization rate of excitons,which help to broaden the recombination zone of electrons and holes.The red OLED device with double-emissive layers achieved a current efficiency of 11.6 cd/A and an external quantum efficiency of 16.3%.Compared with the original device,it has been increased by 1.55 times and 1.81 times.And we optimized the experimental conditions,studying the effect of relatively different thickness of light-emitting layer on the performance of OLED devices and the relationship between the structure of double-emissive layers and excitons blocking layer in limiting excitons diffusion.