Design And Synthesis Of Electron Transporting Materials Based On Anthracene And Their Applications In Blue Electrofluorescent Devices

Organic light-emitting diodes(OLED)technology has been widely used in full-color flexible displays and lighting field,and their products already entered everyone.In particular,as one of the primary colors,blue emission is of great importance in the application of OLEDs.Despite the technology developes quickly,there are still many problems in blue OLED,including the mismatching of carrier mobility of functional materials in the device,which leads to poor stability;the device structure is complex,the preparation cost is high;and the superior blue fluorescent materials are scarce.In order to solve the above problems,the following three aspects are proposed in this paper:(1)Developing novel high-mobility anthracene based electron transport materials(ETMs)to promote the carrier balance in the emitting layer,and then to improve the performance of blue fluorescence devices.(2)Developing multifunctional anthracene based ETMs with blue emission to simplify the structure of devices.(3)Exploring the physical mechanism of the novel anthracene based ETMs in simple device structure,improving the efficiency and reducing the efficiency roll-off.Providing solutions to the problems existing in blue OLED by the above methods.The specific content is as follows:(1)The design strategy of“peripheral modification of bulky steric effect and electron-deficient groups”was proposed.Four anthracene-based ETMs were designed and synthesized,among them,the bulky diazacarbazole with electron-deficient property was used as periphery groups to asymmetrically modify anthracene core.The electron mobility of the four compounds was at the order of 10^-3 cm²V^-1s^-1,and the electron mobility of m-S15NCz DPA reached 3.3×10^-3 cm²V^-1s^-1,ranking in the list of ETMs with high electron mobility.Four compounds were used as ETMs to fabricate sky-blue fluorescent OLED devices.Among them,the device based on m-S15NCz DPA achieved the maximum external quantum efficiency(EQE_max)of 9.00%,which is one of the best devices of the same type at present.Meanwhile,the device based on p-S25NCz DPA achieved the extremely low efficiency roll-off of almost 0%at 50000 cd m^-2.(2)The design strategy of“V-shaped layout of triplet energy levels”was proposed.Four anthracene-based ETMs were designed and synthesized by using high triplet level(E_T)diazacarbazole to modify the anthracene core symmetrically.Due to the increased number of the bulky,electron-deficient 1,5-diazacarbazole(15NCz)and optimization of modification sites,m-D15NCz DPA possesses the best electron transporting performance,and its electron mobility is as high as 5.2×10^-3 cm² V^-1 s^-1,which is 1.5 times that of m-S15NCz DPA in(1).The blue fluorescent OLEDs with four compounds as ETMs obtained excellent performance.In particular,the m-D15NCz DPA-based device exhibited an impressive EQE_max of 8.66%,meanwhile,compared with the m-S15NCz DPA-based device in(1)(The efficiency roll-off was 22.0%at the brightness of 50000 cd m^-2),the efficiency roll-off of the m-D15NCz DPA-based device was reduced(The efficiency roll-off was 13.8%at the brightness of 50000 cd m^-2).(3)Based on the strategy of“bulky peripheral groups enveloping”strategy,in order to make full use of the excellent photoelectric properties of anthracene groups,the large steric hindrance 15NCz and triphenyl/pyridine groups were used to conduct asymmetric modification on its periphery,and two anthracene-based ETMs with high-efficient blue emission were designed and synthesized.Compared with TPBi-based device,the simplified blue fluorescent devices(unilateral homogenous devices)based on two novel compounds achieved better performance,lower turn-on voltage,deep blue emission,and the EQE_max was about 5.80%,which was in the leading level in the efficiency of the same type of unilateral homogeneous devices.(4)Two anthracene-based ETMs with blue emission were designed and synthesized by asymmetrically modifying the anthracene core with bulky,electron-deficient 15NCz and electron-withdrawing diphenylphosphine oxide.Compared with the two compounds in(3),these two compounds possess higher and balanced bipolar carrier transporting performance,higher fluorescence quantum yield(PLQY)and deep blue emission characteristics.Compared with the unilateral homogeneous devices in(3)and TPBi-based devices,these unilateral homogeneous devices with two novel compounds achieved better performance.In particular,the unilateral homogeneous device based on p-PO15NCz DPA showed the best device performance,obtaining deep blue emission with Commission Internationale de L'Eclairage(CIE)coordinate of(0.151,0.066)and EQE_max of 6.40%,the efficiency and light color were at a higher level in the current same type device.Two compounds were used to fabricate the ultra-simple homogeneous devices,in which the p-PO15NCz DPA based device achieved the extremely low efficiency roll-off of 1.3%and 4.8%at 1000 and 5000 cd m^-2,respectively.(5)From single anthracene system to double anthracene system,two different types of double anthracene configurations were constructed.Based on the design strategy“V-shaped layout of triplet energy levels”,two double-anthracene type ETMs were designed and synthesized by using bulky 15NCz monomer with large steric hindrance and high E_T to carry out peripheral modification.The electron mobility values of the two compounds are in order of 10^-4?10^-3 cm²V^-1s^-1,and their thermodynamic stability is good.For the first time,two novel double-anthacene based compounds were used as ETMs and self-synthesized p-3Cz15NCz Tz as blue fluorescent guest to fabricate blue OLED devices.Compared with traditional electron transport material TPBi based device,these devices based on two novel double-anthacene based compounds achieved EQE_maxof around 10%and blue electroluminescence peak of about 470 nm.Based on the above research,the newely-developed ETMs and multifunction ETMs with both blue light emission provide effective solutions to simplify the device structure and improve the performance of blue fluorescence devices,and also provide strategies and lay a foundation for the subsequent design of multifunction organic materials.