【摘要】：基于熱活化延遲熒光(TADF)機(jī)制的有機(jī)發(fā)光二極管(OLED)由于采用不含銥、鉑等貴重金屬的純有機(jī)熒光材料,可以利用三重態(tài)到單重態(tài)的逆系間竄越(RISC)過(guò)程,實(shí)現(xiàn)100%的激子利用率,經(jīng)過(guò)近幾年的發(fā)展,TADF-OLED的器件外量子效率(EQE)已接近甚至超過(guò)磷光器件的水平。TADF材料不僅具有低成本的優(yōu)勢(shì),同時(shí)其既可以作為發(fā)光材料也可以作為主體材料而實(shí)現(xiàn)多功能應(yīng)用,已被視為下一代OLED材料而得到廣泛研究,但目前還面臨一些亟需解決的問(wèn)題。一方面,紅光TADF材料還很缺乏,其器件的性能也遠(yuǎn)遠(yuǎn)落后于藍(lán)光和綠光TADF器件。紅光TADF材料的設(shè)計(jì)合成和器件構(gòu)筑對(duì)研究者來(lái)說(shuō)仍然是一項(xiàng)充滿挑戰(zhàn)的工作。另一方面,TADF器件在高亮度或高電流密度下由于三重態(tài)-三重態(tài)激子或單重態(tài)-三重態(tài)激子湮滅等原因存在嚴(yán)重的效率滾降問(wèn)題。因此,在TADF分子設(shè)計(jì)上,需要進(jìn)一步拓展其材料體系,并詳細(xì)研究其光物理機(jī)制,以期得到高性能和穩(wěn)定的紅光TADF材料。在器件構(gòu)筑方面,需要開(kāi)發(fā)新的器件結(jié)構(gòu)和制備方法,深刻認(rèn)識(shí)器件的物理過(guò)程,以期提高性能,改善壽命,最終實(shí)現(xiàn)產(chǎn)業(yè)化應(yīng)用的高效穩(wěn)定的TADF電致發(fā)光器件。本論文主要是以二氰基取代的芳香共軛衍生物作為受體基團(tuán)構(gòu)建新型的熱活化延遲熒光材料體系,重點(diǎn)開(kāi)展了以下幾方面的研究工作:1、在第二章中,我們通過(guò)簡(jiǎn)單的反應(yīng)合成了基于二氰基取代菲并吡嗪(DCPP)受體和三苯胺給體的D-π-A-π-D型的近紅外TADF材料。理論計(jì)算表明其HOMO/LUMO分布方式具有大部分分離的特征,有利于得到小的單重態(tài)-三重態(tài)能級(jí)差(ΔEST≈0.20 e V)。另外,HOMO/LUMO在DCPP受體核上還有小部分重疊,有利于獲得較高的振子強(qiáng)度(f≈0.1508),以增強(qiáng)輻射躍遷速率。因此,這種分子設(shè)計(jì)可以同時(shí)獲得小的ΔEST和高的輻射躍遷速率。其非摻雜薄膜光譜發(fā)射峰位為708 nm,熒光量子效率為14%,在近紅外熒光化合物處于較高水平。我們首次制備了近紅外發(fā)光的TADF器件。其中非摻雜器件最大EQE達(dá)2.1%,CIE坐標(biāo)為(0.70,0.29)。摻雜器件發(fā)光峰位為668 nm,最大外量子效率達(dá)9.6%,接近一些類似光譜的近紅外磷光OLED的水平。此項(xiàng)研究工作為開(kāi)發(fā)高效的近紅外TADF材料提供了一些設(shè)計(jì)思路。2、在第三章中,我們研究了不同給體基團(tuán)對(duì)TADF材料性質(zhì)的影響。我們通過(guò)在DCPP受體核上,連接不同給體取代基團(tuán)如咔唑(Cz)、二苯胺(DPA)和二甲基吖啶(DMAC),合成了三個(gè)D-A-D型的TADF化合物。采用苯環(huán)作為π-橋,合成了另外兩個(gè)D-π-A-π-D型TADF化合物。這些化合物實(shí)現(xiàn)了黃光至深紅光的發(fā)射。其中以DMAC為給體的化合物具有最大的D-A扭曲角,其表現(xiàn)了較小的ΔEST和短的延遲熒光壽命。采用雙極性分子為主體制備了黃光至深紅光發(fā)射的TADF器件。其中黃光器件效率可達(dá)47.6 cd A~(-1)(14.8%),橙光器件效率可達(dá)34.5 cd A~(-1)(16.9%),深紅光器件效率可達(dá)13.2 cd A~(-1)(15.1%)。然而以Cz和DPA為給體的化合物作為發(fā)光層的器件由于大的ΔEST和長(zhǎng)的延遲熒光壽命導(dǎo)致了顯著的效率滾降。因此設(shè)計(jì)紅光TADF分子時(shí),除了確保高的熒光量子效率外,還應(yīng)進(jìn)一步減小ΔEST和延遲熒光壽命來(lái)降低激子淬滅,從而得到低效率滾降的器件。3、在第四章中,為了調(diào)控TADF分子的發(fā)光波長(zhǎng),使其進(jìn)一步紅移,我們通過(guò)拓展DCPP受體核的π共軛,使受體核的吸電子能力增加、LUMO能級(jí)降低,實(shí)現(xiàn)了這一目的。通過(guò)連接二苯胺(DPA)或二甲基吖啶(DMAC)作為給體基團(tuán),我們得到了兩個(gè)紅光至近紅外的TADF化合物。理論計(jì)算的能級(jí)軌道分布表明,拓展DCPP受體核的π共軛后,分子的LUMO能級(jí)降低了0.25~0.28 e V,而HOMO能級(jí)基本不變,因此禁帶降低,光譜紅移。兩個(gè)化合物的非摻雜薄膜光譜峰位均為765 nm,相比于第二章的化合物紅移近60 nm。其中以DPA為給體的分子制備的摻雜OLED器件,發(fā)光峰位在708 nm,最大EQE為5.4%,為目前報(bào)道的熒光近紅外器件的最高效率之一。這一結(jié)果表明,延長(zhǎng)受體核的π共軛長(zhǎng)度以及增加其吸電子能力是實(shí)現(xiàn)紅光至近紅外TADF發(fā)射的有效策略。4、在第五章中,我們采用二氰基取代的綠光TADF材料4Cz IPN作為敏化主體材料,喹吖啶酮衍生物作為客體摻雜劑,利用逆系間竄越(RISC)和F?rster能量轉(zhuǎn)移(FRET)過(guò)程,使在TADF主體上產(chǎn)生的三重態(tài)激子能量能被傳統(tǒng)熒光材料捕獲,有效提高了熒光器件的激子利用率�；诖瞬呗灾苽涞腛LED器件最大EQE和功率效率分別達(dá)到14.6%和53.4 lm W-1,高于傳統(tǒng)熒光型OLED器件的最大效率值近三倍。并且由于主客體之間的快速能量轉(zhuǎn)移使主體上的三重態(tài)激子密度降低,器件的效率滾降很小,在亮度為1000 cd m-2下,EQE仍能為13.7%。這種方法不僅提高了傳統(tǒng)熒光OLED的效率,而且有助于獲得低效率滾降和高色純度的TADF電致發(fā)光器件。綜上所述,我們?cè)O(shè)計(jì)合成了一系列基于二氰基取代芳香共軛受體的黃光至近紅外光TADF材料,并系統(tǒng)研究了材料結(jié)構(gòu)與物理性質(zhì)的關(guān)系,進(jìn)一步拓展和豐富了紅光TADF材料體系;在器件構(gòu)筑上,我們采用二氰基取代的TADF材料作為傳統(tǒng)熒光材料的敏化主體,基于能量轉(zhuǎn)移過(guò)程,實(shí)現(xiàn)了效率遠(yuǎn)超傳統(tǒng)熒光器件的高效率且低滾降的電致發(fā)光器件,對(duì)進(jìn)一步開(kāi)發(fā)高效的熱活化延遲熒光材料與器件體系起到了積極的促進(jìn)作用。
[Abstract]:The organic light-emitting diode (OLED) based on the heat-activated delayed fluorescence (TADF) mechanism can realize 100% exciton utilization by using a pure organic fluorescent material containing noble metals such as platinum and platinum, In recent years, the external quantum efficiency (EQE) of the TADF-OLED has been close to or even higher than that of the phosphorescent device. The TADF material not only has the advantage of low cost, but also can be used as a light-emitting material and can be used as a main material to realize the multi-function application, and has been regarded as the next-generation OLED material to be widely researched. In one aspect, that red TADF material is also scarce, and the performance of the device is well behind the blue and green TADF devices. The design and synthesis of the red TADF material and the construction of the device remain a challenging task for the researchers. On the other hand, the TADF device has serious efficiency roll-down problems due to triplet-triplet exciton or singlet-triplet exciton annihilation at high brightness or high current density. Therefore, in the design of the TADF molecule, it is necessary to further expand its material system, and to study its optical physical mechanism in detail with a view to obtaining high-performance and stable red-light TADF material. In the aspect of device construction, a new device structure and a preparation method are needed, and the physical process of the device is deeply realized, so that the performance is improved, the service life is improved, and the highly efficient and stable TADF electroluminescence device of the industrial application is finally realized. The thesis mainly focuses on the following aspects:1. In the second chapter, A near-infrared TADF material based on dicyano-substituted phenanthrene (DCPP) receptor and triphenylamine donor was synthesized by a simple reaction. The theoretical calculation shows that the HOMO/ LUMO distribution mode has a large part of the separation characteristics, and is favorable for obtaining the small singlet-triplet energy level difference (CREST-0.20e V). In addition, the HOMO/ LUMO has small partial overlap on the core of the DCPP receptor, which is favorable for obtaining higher transducer intensity (f = 0.1508) to enhance the radiation transition rate. Thus, such a molecular design can simultaneously obtain a small CREST and a high radiation transition rate. Its non-doped thin-film spectral emission peak is 708 nm, the fluorescence quantum efficiency is 14%, and the near-infrared fluorescent compound is at a higher level. For the first time, a near-infrared light-emitting TADF device was prepared. In which the maximum EQE of the non-doped device is 2.1% and the CIE coordinates are (0.70, 0.29). The emission peak of the doped device is 668 nm, the maximum external quantum efficiency is up to 9.6%, and the level of the near-infrared phosphorescent OLED similar to the spectrum is close to. This study provides some design considerations for the development of an efficient near-infrared TADF material. In chapter 3, we have studied the effects of different donor groups on the properties of the TADF material. Three D-A-D-type TADF compounds were synthesized by connecting different donor substituent groups, such as Cz, diphenylamine (DPA), and dimethyl disulfide (DMAC) on the DCPP receptor core. Two additional D-A-A-1-D-type TADF compounds were synthesized by using a benzene ring as a 1-bridge. These compounds achieve the emission of yellow to deep red light. In which the compound with dmac as the donor has the greatest d-a twist angle, which exhibits a small bEST and a short delay fluorescence lifetime. TADF devices with yellow to deep red light are prepared by using bipolar molecules as the main body. The efficiency of the yellow light device can reach 47.6 cd A-(-1) (14.8%), the efficiency of the orange-light device can reach 34.5 cd A-(-1) (16.9%), and the efficiency of the deep red light device can reach 13.2 cd A-(-1) (15.1%). However, the device taking Cz and DPA as the donor as the light-emitting layer resulted in significant efficiency roll-off due to large ESTs and long delayed fluorescence lifetime. Therefore, in designing the red TADF molecule, in addition to ensuring high fluorescence quantum efficiency, the exciton quenching can be further reduced by reducing the fluorescence lifetime of the TADF and the delay, so as to obtain a low-efficiency roll-off device. The purpose of this is to increase the electron-withdrawing ability of the receptor core and to decrease the LUMO level by expanding the cohomology of the nuclear of the DCPP receptor. By connecting diphenylamine (DPA) or dimethyl disulfide (DMAC) as a donor group, we obtained two red to near-infrared TADF compounds. The energy level orbit distribution of the theoretical calculation shows that the LUMO level of the molecule is reduced by 0.25-0.28e V, while the HOMO energy level is substantially unchanged, so that the forbidden band is reduced and the spectrum is red shifted. The spectral peak of the non-doped thin film of the two compounds was 765 nm, and the red shift of the compound in the second chapter was nearly 60 nm. The light-emitting peak is at 708nm and the maximum EQE is 5.4%, which is one of the highest efficiency of the currently reported fluorescent near-infrared device. The results of this study show that the effective strategy for the emission of red-to-near-infrared TADF is the extension of the cohomology length of the receptor core and the increase of its electron-absorption ability. In the fifth chapter, we use the green TADF material 4Cz IPN which is a two-cyano-substituted green-green TADF as the sensitizing main material. The energy of the triplet exciton generated on the main body of the TADF can be captured by the conventional fluorescent material, and the exciton utilization rate of the fluorescent device can be effectively improved. The maximum EQE and power efficiency of the OLED device prepared based on this strategy reach 14.6% and 53.4 lm W-1, respectively, which is nearly three times higher than the maximum efficiency value of the conventional fluorescent OLED device. And due to the rapid energy transfer between the main objects, the triplet exciton density on the main body is reduced, the efficiency of the device is small, and the EQE can still be 13.7 percent under the brightness of 1000 cd-2. The method not only improves the efficiency of the conventional fluorescent OLED, but also helps to obtain a TADF electroluminescent device with low efficiency and high color purity. In conclusion, we have designed a series of yellow-to-near-infrared (TADF) materials based on dicyano-substituted aromatic co-organic receptors, and systematically studied the relationship between the structure and physical properties of the materials, and further developed and enriched the red-light TADF material system; on the device construction, By adopting the TADF material substituted by the dicyano as the sensitizing main body of the traditional fluorescent material, the invention realizes the high-efficiency and low-roll-down electroluminescent device with the efficiency and the ultra-conventional fluorescent device based on the energy transfer process, And has a positive effect on the further development of the high-efficiency heat-activation delayed fluorescent material and the device system.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TQ422

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