Study On The Structure Design And The Performance Enhancement Of Blue Organic Light-emitting Devices

Organic light emitting devices (OLED) have a widely application in the field of flatpanel display and solid state lighting due to its advantages of high brightness, low powerconsumption and panel emitting etc. As the application in lighting and display, it’s importantto design Monochromatic light devices with high performance and simple production process.This work focuses on blue OLED, in order to enhance the efficiency, the luminance and thestabilization of color coordinate of blue OLED. By structure design, we analyze the workingmechanism of carrier and related device principle. On the basis of these experiments, wefabricate different types of blue devices with the enhancement in efficiency, luminance andcolor coordinate:1. Designing non-doped devices with single emitting layer. By the experiments of holeonly devices and electron only devices, we clarify that DNCA prefer hole transport. we inserta 5 nm BAlq between emitting layer and electron transporting layer (ETL) as excitonfeedback layer, this layer can block holes meanwhile expand exciton width, the efficiencyincrease to 4.2 cd/A from initial 2.9 cd/A, max luminance increases to 24,600 cd/m~2frominitial 14,000 cd/m~2. The benefit from this layer is avoiding exciplex emission, the coordinateof this device shift only from (0.147, 0.304) to (0.146, 0.297). In order to adjust hole carrier,we insert ADN layer with high HOMO in emitting layer. with thickness of 4 nm, theefficiency increases to 5.9 cd/A, max luminance increase to 16,170 cd/m~2. We also insert 0.8nm LiF in ETL, at different voltage, the device express different electron increase mechanism,two mechanisms both increase electron injection to emitting layer, facilitate carrier balance,and enhance the performance of the device.2. Introducing p-n heterojunction device. By studing the n-dopant and p-dopant deviceswith different concentration, we find that exciton can exist in both sides of the heterojunction,and these devices favor low concentration. So we fabricate different concentration doubleemitting layer heterojuntion devices. At concentration of 3%, with a turn-on voltage of 2.6 Vat 1 cd/m~2, this type of OLED presents a maximum luminance efficiency of 8.83 cd/A at5.818 mA/cm~2and a maximum luminance of over 40,000 cd/m~2.3. Fabricating highly performance doped single emitting layer device. Firstly, wefabricate devices with the emitting of host and guest separately, find the factors limiting thecharacter of devices. Secondly, with different concentration guest doped in host, we fabricatesingle doped emitting layer device. Due to the excellent molecule space structure, thiscombination can decrease concentration quenching. with concentration of 6%, the device reaches current efficiency of 14 cd/A, its max luminance exceeds 60,000 cd/m~2.