Study On The Performance Of Tandem Organic Light-Emitting Devices With Low Driving Voltage And High Efficiency

In recent years,organic light-emitting device?OLED?has made rapid and brilliant progress in the field of display and lighting.However,there are a few key issues for improving of the device's efficiency and stability in the process of promoting the commercialization of OLED.Among the various device's structures,tandem OLED presents the higher brightness,efficiency and stability compared to that of the traditional device,which has been attracting the worldwide attention.But the driving voltage of tandem OLED is still high,and current efficiency of the device can not be enhanced to a greater extent.In this work,during the fabrication of single-emitting unit of OLED,we mainly focused on optimization of the carrier injection,transport and balance of recombination to improve the performance of OLED.Moreover,based on the structure of composite electronic buffer layer,we designed a novel efficient charge generation layer to achieve high performance tandem OLED with low driving voltage and high efficiency.The main contents are listed as follows:1.Firstly,we fabricated the OLED by inserting the thin layer of alkali metal chloride NaCl into the hole transport layer NPB.The amount of hole injection ability could be adjusted by optimizing the thickness of NaCl layer.The current efficiency of OLED is improved effectively.The maximum current efficiency of the optimal device is 5.3 cd/A,which is increased by 29.3% compared to that of conventional device?4.1 cd/A?.Then,the performance of OLED is improved by inserting non-doped electronic buffer layer TCNQ between electron transport layer Bphen and the cathode.The maximum luminance,current efficiency and power efficiency of the optimal device are increased by 37.1%,50.8% and 162.5%,respectively,compared with those of the control device without electronic buffer layer TCNQ.This improvement can be attributed to that TCNQ layer not only smooth the surface of the films but also improve the electronic injection and transport characteristics by optimizing the thickness of TCNQ layer.Finally,the maximum current efficiency?6.9 cd/A?of the optimal device is increased by 68.3%,compared with that of conventional device?4.1 cd/A?.This improvement can be attributed to that the insertion of NaCl/Mg electronic buffer layer,which is a simple approach can balance of holes and electrons in emission layer.As a result,the current efficiency of the OLED can be effectively improved.2.The introduction of a novel non-doped charge generation layer NaCl/Mg/MoO₃/NPB in tandem OLED,which the injection ability of electrons can be improved effectively by the electronic buffer layer NaCl/Mg.Firstly,the mechanism of the effective charge generation layer is discussed by the device with electron-only and the device with hole-only.Meanwhile,the DNCA was used as blue luminescent material.For this tandem device,the current efficiency of 8.1 cd/A is enhanced approximately by 2.5 times compared with those of the single-emitting unit of OLED?3.2 cd/A?,while the driving voltage is about 1.6 times higher than those of the reference device.Then,by optimizing the thickness of NaCl and Mg in the charge generation layer,the current efficiency?21.8 cd/A?of the tandem device is effectively enhanced by 6.8 times compared with those of the single-emitting unit device.Finally,in order to verify the general applicability of the charge generation layer,the optimized NaCl/Mg/MoO₃/NPB was applied to the tandem OLED with Alq₃ as the green luminescent material.The current efficiency of the device will continue to increase with the increase of the light-emitting unit,while the device's driving voltage will not be doubled improvement.