Study On The Optoelectronic Properties Of Blue OLED Devices Based On TADF Co-Doping

Organic light-emitting diode(OLED)has attracted wide attention because of its self-luminous,fast response speed,pure chromaticity,low driving voltage,low energy consumption,flexibility and high efficiency.One of the hot research directions in the field of display and lighting at home and abroad.Red,green and blue are the basic colors in OLED research,and the photoelectric performance of blue OLED lags behind the other two colors.The method of adopting host-guest doped structure is considered to be one of the effective ways to improve the performance of blue OLED devices.In devices with host-guest doped structure,there are two emission mechanisms:exciton energy transfer and carrier trapping.Among them,the type of host material and guest doping concentration are the constraints of these two light-emitting principles.Therefore,selecting the appropriate host material and guest doping concentration is a very important task for the preparation of high-efficiency and stable blue light devices.Thermally Activated Delayed Fluorescence(TADF)material,as a third-generation luminescent material,has the advantages of higher efficiency,higher brightness and no pollution than the previous two generations,but how to maximize the efficiency of this material is scientific research difficulties in the process.In this paper,an efficient and stable blue TADF luminescent material,DMAC-DPS,is selected as the guest dopant,and mCP,PPF and DPEPO are used as the host material.Three different types of host and guest structure devices are prepared and studied.Based on its photoelectric performance,the main work is summarized as follows:First,based on mCP,the experimental basic device was prepared by vacuum thermal evaporation method,and the specific structure of the experimental device was determined by structure optimization experiment:MoO₃(1nm)/TAPC(40nm)/mCP(10nm)/[mCP:DMAC-DPS](30nm)/PPF(10nm)/TPBi(40nm)/LiF(0.8nm)/Al(100nm),later experiments only changed mCP to PPF and DPEPO,and adjusted the doping concentration.Second,fix the guest doping concentration(30%),choose three host materials to prepare blue OLED devices,study the voltage-current density,brightness,external quantum efficiency and current efficiency and other optoelectronic properties,and draw the following conclusions:The turn-on voltage difference is very small.The device with mCP as the main body exhibits the lowest brightness of 12759.65cd/m²and the lowest EQE value of 6.77%.The maximum brightness of the device with PPF and DPEPO as the main body is 47.41%and 49.23%higher than that of the mCP device,respectively.At the same time,the internal quantum efficiency of DPEPO is higher than that of PPF,making the EQE value and maximum brightness value of its device larger than that of the PPF main device.Third,studying the influence of the guest concentration on the photoelectric performance of the three host-guest doped blue OLED devices,it is concluded that the efficiency peak of the mCP host blue light device appears at the guest concentration of30%,and the maximum brightness of the device is 12759.65cd/m².The maximum EQE value is 6.77%;the efficiency peak of the PPF host blue light device appears at the guest concentration of 50%,the maximum brightness of the device is 19544.51cd/m²,and the maximum EQE value is 12.3%;the efficiency peak of the DPEPO host device appears at the guest concentration of 50%,the maximum brightness of the device is19570.82cd/m²,and the maximum EQE value is 15.3%.The optical and electrical properties of the three host-guest structure devices are quite different,but the EL peak position of each device is stable at 490nm from the EL spectrum,and no other impurity peaks are generated,indicating that there are carriers between the three host materials and the guest.The captured luminescence is weak,and energy transfer is the main focus.Fourth,the life test of blue OLED devices with three host-guest doped structures was carried out.It was found that with the increase of doping concentration,the half-life of mCP and DPEPO devices showed a trend of first increasing and then decreasing,and the optimal lifetime doping concentration was respectively It is 30%and 50%,and the half-life of PPF device shows a monotonous decrease with the increase of doping concentration,and the optimal doping concentration for lifetime is 10%.Dark spots are found in the light-emitting area of the device through a microscope,and the dark spots in the high-concentration doped device are more concentrated.