Study On The Efficiency Roll-off Of Single-layer Organic Light-emitting Devices

Organic light-emitting devices(OLED)are considered to be the core of the next generation flat display technology because of their many virtues.The advantages of OLED are mainly independent light-emitting,thin and soft,surface light source,etc.Many producers and researchers input a lot of financial resources and manpower to the research of them,which have made a big breakthrough.But,there still exist many difficulties for the OLED to achieve the completely commercialization.In general,the structures of OLED are quite complex,which not only greatly improved the difficulty of the production process,also caused the high cost of production.In this paper,we made a single OLED with high performance through the ingenious use of doping method.First of all,we made a very simple single-layer OLED.Orange phosphorescent material PO-01 served as emission dye for the high efficiency;CBP with good hole and electron transport mobilities served as the host material.By changing the thickness of the modified layer of cathode,analysing the current density,current efficiency,etc.,we know the influence of the modified layer Liq for OLED performance.When the cathode modified layer thickness of Liq is 1 nm,OLED shows the best performance,the maximum current efficiency of device reached 16.34cd/A.Introduction of cathode modification Liq effectively promoted the electron injection,improve the performance of the device.However,device represents pretty high efficiency roll-off of 9.11%and 25.58%at the luminance of 5000 cd/m~2 and 10000 cd/m~2.Then,we explore the excitons recombination zone of the device.By changing the location of red phosphorescent ultra-thin layer and observing the red glow,we know that the excitons recombination zone is predominantly close to anode side.As the excitons recombination zone has been determined,we doped FIrPic into organic layer,which improved the device performance significantly.By further optimizing the thickness of organic layer,the highest current efficiency of device reached 31.38 cd/A.The efficiency roll-off of device also got further improvement.Device represents much lower efficiency roll-off of 1.97%and 4.46%at the luminance of 5000 cd/m~2 and 10 000 cd/m~2,which are much lower than the previous device.Finally,to investigate the influence of FIrPic on the transport properties of single-layer OLED,we fabricated hole-only and electron-only devices.We found that doping FIrPic into CBP facilitates the transport of hole and the injection of electron.