Research On Improving The Efficiency Roll-off Of OLED With Using Bipolar Host Material And The Stack Structure

With the rapid development of modern society and the advent of 5G era,people have a higher demand for data display.The most promising display technique is organic light-emitting diodes?OLED?in the 21st century.OLED has been attracting a lot of attention for its advantages to be the project for researcher.The Traditional OLED lose a lot of energy without using triplet excitons.As the phosphorescent OLED was presented,it can make full use of singlet and triplet to realize high efficiency.However,the rolling off has been a new challenge in the phosphorescent OLED.In this paper,phosphorescent materials were doped in fluorescent materials which have characteristics of bipolar transmission to reduce efficiency roll-off by energy transfer.On the other hand,we had investigated a tandem warm white OLED which has great color coordinate based on the microcavity effect.And optical performance of it were explored in detail.The main research contents of this paper are listed as below.1.An highly efficient tandem OLED was realized by employing multilayer structure of CsN3/Al/HAT-CN as charge generation unit?CGU?.The charge generation and transporting processes within CGU were discovered by analyzing electroluminescence properties of the fabricated dual-color tandem device with yellow and green emissions.The Experimental data declare that the charge were generated at the interface of HAT-CN and NPB.The Al can improve the injection ability of electron in CGU.The maximum efficiencies of tandem device are as high as6.4 cd/A and 2.3 lm/W,respectively.Luminance,the current efficiency and voltage of tandem device are about 2-fold of corresponding single-unit device at the same current density.2.An Highly efficient phosphorescent OLED were fabricated with co-doping mTPA-PPI and PO-01.We found the optimum concentration of doping is 8%by analyzing the absorption spectrum and excited spectrum.The maximum efficiencies of device are 48.36cd/A and 45.26lm/W,respectively.The luminance is as high as105900cd/m².And the J₀ is 317.57mA/cm²,which indicates low efficiency roll-off.The results reveal that the PO-01 have two characteristics of carrier transport and carrier trapping at the same time with doping in the mTPA-PPI.At low doping concentration,carrier trapping is dominant,and with the increase of doping concentration,the transmission characteristics will be enhanced.The excitons which are captured or transmitted by PO-01 can recombine on PO-01 directly.3.An highly efficient tandem warm white OLED with stable color coordinates was designed based on mTPA-PPI and PO-01.We found there is microcavity effect in the tandem device.But the change of color coordinates is only?5.98%,5.62%?,which indicates that the existence of the microcavity effect has not affected its practical value.In the end,the reason for the spectrum variation of this device was explained by analyzing microcavity effect.