三苯甲基类中性自由基的合成及其电致发光性能研究—突破OLED内量子效率25%上限的新途径

发布时间：2018-03-03 21:45

本文选题：有机电致发光　切入点：有机中性自由基　出处：《吉林大学》2017年博士论文　论文类型：学位论文

【摘要】：在显示和照明领域中,有机电致发光器件(OLED)的应用是一件开创性的工作,OLED器件集成了自发光、全视角、可弯曲、能耗低等诸多优势,逐渐成为显示和照明领域的领跑者。然而,有机电致发光器件的研究仍然存在一些关键性问题。比如,如何在降低材料成本的同时又有效利用不发光的三线态激子等。虽然磷光材料能够有效地解决荧光OLED中三线态激子利用难的问题,从而实现100%器件内量子效率(IQE),但是贵重金属的磷光材料价格昂贵,并且难以获得能够达到欧洲广播联盟(EBU)标准的深蓝磷光材料。最近,热致延迟荧光(TADF)材料解决了OLED材料价格昂贵的问题,实现了荧光分子中三线态激子的有效利用,从而获得了IQE为100%的OLED器件。除此之外,研究报道显示,通过三线态-三线态淬灭(TTA)和杂化局域电荷转移激发(HLCT)态等途径也可以有效利用三线态激子实现高效率发光。虽然上述方法具备的优点进一步推进了OLED的发展,但是存在的一些问题仍需要我们继续探索,以获得廉价、高效率的材料与器件。因此,本论文讨论了OLED的发展状况、工作原理、不同类型OLED发光材料及其发光原理和优缺点。为了解决三线态激子难以利用和材料价格昂贵等问题,与其他发光机理不同,我们提出了有机中性自由基双重态发光机理。从发光机理来看,磷光、TADF、TTA或者HLCT,都围绕着“三线态激子利用”的问题展开研究。与上述工作都不同,本论文中提出了双重态发光原理。由于有机中性自由基(有机开壳分子)分子最外层只有一个单电子,根据量子力学原理,单个未成对电子的自旋组态为双重态。这种双重态激子跃迁返回基态时,不会受到电子自旋禁阻的限制。因此,理论上以有机开壳发光分子作为发光材料的OLED器件内量子效率能够达到100%。因此,我们以研究有机中性自由基双重态激子发光机理为目标,重点进行了以下几方面的工作:1.我们选择稳定且发光的三(2,4,6-三氯苯基)甲基自由基(TTM),根据相关文献报道适当优化反应条件,通过与咔唑反应,成功合成出对应的中性自由基TTM-1Cz和TTM-2Cz。两类自由基均表现出良好的热稳定性(热分解温度均在330℃以上)和较高的发光效率。其中TTM-1Cz和TTM-2Cz在正己烷溶液中的发射峰分别位于628 nm和640 nm,处于深红光区,荧光量子效率分别为53%和54%。研究其光物理性能发现,三种自由基的发光都来自于双重态,不同之处是TTM的发光来自于局域态,而TTM-1Cz和TTM-2Cz的发光来自于CT态的双重态发光。光稳定性实验结果表明TTM、TTM-1Cz和TTM-2Cz的半衰期分别为1.6×102 s、9.9×103 s和4.7×105 s,随着咔唑数量增多稳定性大幅提高。其次,我们以CBP作为母体,制备了掺杂浓度为5%的中性自由基发光OLED器件,TTM-1Cz和TTM-2Cz的掺杂器件的最大EQE效率分别达到2.4%和0.8%,EL谱峰值波长处于693 nm和690 nm。磁场效应实验结果进一步证明器件的发光来自于双重态发光。2.通过优化自由基的器件结构,利用自由基和前体的混合物,初步实现了双重态激子发光OLED器件,双重态激子的生成比例(χD)接近于100%。为了进一步研究混合物(前体和自由基)的性能和准确调控自由基的掺杂比例,我们合成出TTM-1Cz和TTM-2Cz的前体(αHTTM-1Cz和αHTTM-2Cz)。通过研究其光物理性能发现,自由基前体均为宽能隙且具有较低发光效率的闭壳分子。研究不同掺杂浓度的自由基TTM-1Cz和前体αHTTM-1Cz的OLED器件发现,前体和自由基的掺杂不仅改善了自由基的聚集淬灭,而且提高了器件性能。其中TTM-1Cz自由基在前体中掺杂浓度为2.5%时器件EQE达到10.5%,EL光谱峰值波长为666 nm,是非磷光材料作为发光层的深红光荧光器件中EQE的最高值。这种准确调控自由基前体和自由基的主-客体掺杂方式,证明中性自由基发光的OLED器件内量子效率上限能达到100%,并且是解决自由基聚集淬灭的新方案。3.为了研究影响自由基稳定性和光物理性能的因素,我们通过在咔唑3,6位上引入缺电子基团苯甲酰基和富电子基团叔丁基,与自由基TTM反应得到两种新自由基TTM-1Cz Bz和TTM-1Czt B。两种自由基都表现出较高的热稳定性(热分解温度均330℃),研究发现,TTM-1Cz Bz和TTM-1Czt B在正己烷溶液中的发射峰分别在614 nm和640 nm处出现,与TTM-1Cz相比分别蓝移14 nm和红移12nm,荧光量子效率分别为54%和55%。实验结果表明:咔唑上缺、富电子基团的引入不仅影响自由基的光物理性能而且对自由基的光稳定性具有很大的影响。与TTM-1Cz相比,TTM-1Cz Bz的光稳定性降低15倍左右,而TTM-1Czt B的光稳定性比TTM-1Cz高4.5倍以上。研究自由基器件单载流子迁移率发现,缺电子基团苯甲酰基使得自由基电子迁移率提高,而给电子基团叔丁基导致器件空穴和电子迁移率均有所降低。最终,我们制备了以两种自由基(TTM-1Cz Bz和TTM-1Czt B)作为发光客体5 wt.%掺杂于CBP中的OLED器件,最大外量子效率分别达到5.2%和2.8%。其中TTM-1Czt B掺杂器件的EL光谱峰值波长在745 nm。
[Abstract]:In the display and lighting in the field of organic electroluminescent devices (OLED) application is a pioneering work, the OLED device integrates self luminous, wide viewing angle, can be bent, the many advantages of low energy consumption, has become a leader in the field of display and lighting. However, there are still some key problems of electromechanical induced the light emitting device. For example, how to reduce the material cost and the effective use of no light of three excitons. Although phosphorescent materials can effectively solve the difficult problem of three excitons by fluorescence OLED, thus realizing the 100% device internal quantum efficiency (IQE), but the price of expensive precious metal phosphorescent materials it is difficult to obtain, and can reach the European Broadcasting Union (EBU) blue phosphorescent material standard. Recently, the heat induced delayed fluorescence (TADF) material to solve the problem of expensive OLED material, the fluorescent molecule three triplet excitation The effective use of the thus obtained IQE devices for 100% OLED. In addition, the research report shows that by three - three triplet triplet quenching (TTA) and hybrid local charge transfer excited state (HLCT) approach can also be effective use of three excitons to achieve high efficiency light. Although the advantages of the method with the further development of OLED, but some problems still need to continue to explore, to obtain cheap materials and devices with high efficiency. Therefore, this paper discusses the development status of OLED, the working principle of different types of OLED luminescent material and luminescent principle and advantages and disadvantages. In order to solve the problem of three excitons it is difficult to use and the materials are expensive, unlike other luminescence mechanism, we propose a light-emitting organic neutral radical doublet mechanism. From the light emitting mechanism, phosphorescence, TADF, TTA or HLCT, all around three triplet excitation Study on using "problem. Different from the above work, this paper proposes a dual state luminescence principle. Because the organic neutral radical (organic open shell molecules) the outermost molecular only a single electron, according to the principle of quantum mechanics, single unpaired spin group electronic states as a doublet. This dual state excitontransition return to the ground state, not by the electron spin forbidden limit. Therefore, the theory of open shell to organic light emitting molecule OLED devices as luminescent materials internal quantum efficiency can reach 100%. so we to study organic neutral radical double exciton luminescence mechanism as the goal, focus on the following aspects: 1. selection of stable and light (three 2,4,6- three chlorophenyl) methyl radical (TTM), the appropriate reaction condition optimization according to the related literature reports, with the successful synthesis of carbazole reaction, since the corresponding neutral By TTM-1Cz and TTM-2Cz. two kinds of free radicals showed good thermal stability (thermal decomposition temperature at 330 DEG C) and high luminous efficiency. The TTM-1Cz and TTM-2Cz emission peaks in hexane solution are located at 628 nm and 640 nm, in a deep red zone, the fluorescence quantum efficiency were 53% and the 54%. study found its photophysical properties, emitting three free radicals from the dual state, the difference is that TTM light from the local state, and the state of TTM-1Cz and TTM-2Cz dual luminescence from CT state light. Light stability of the experimental results showed that TTM, TTM-1Cz and TTM-2Cz has a half-life of 1.6 * 102 s respectively. 103, 9.9 * s and 4.7 * 105 s, with the increase in the number of carbazole stability to enhance largely. Secondly, we take CBP as the parent, was prepared by doping concentration of neutral radical 5% light emitting devices of OLED, maximum EQE and TTM-2Cz of the TTM-1Cz doped device The efficiency reached 2.4% and 0.8%, the peak wavelength of EL spectrum at 693 nm and 690 nm. from the experimental results further prove that the magnetic field effect devices emitting from dual state luminescence by.2. device structure optimization of free radicals, the use of a mixture of free radical and precursor, realized the double exciton luminescence of OLED devices, the proportion of double exciton generation the (x D) close to 100%. in order to further study the mixture (precursor and radical) doping ratio performance and accurate regulation of free radicals, we synthesized precursor TTM-1Cz and TTM-2Cz (HTTM-1Cz alpha and alpha HTTM-2Cz). Through the study of their photophysical properties found that free radical precursors are wide bandgap and it has low luminous efficiency of closed shell molecules. OLED devices of different doping concentration of free radicals and TTM-1Cz precursor alpha HTTM-1Cz, precursor and free radical doping not only improved the free radical quenching and aggregation. And improve the performance of the device. The TTM-1Cz free radicals in a precursor doping concentration of 2.5% EQE to 10.5% EL devices, peak wavelength is 666 nm, is non phosphorescent materials as the highest value of deep red fluorescence luminescence layer in EQE. The main object of the accurate control of radical doped precursors and free the proof of the neutral radical OLED light emitting device of the internal quantum efficiency limit can reach 100%, and is the new.3. solution free radical aggregation quenching in order to study the factors affecting the stability of free radicals and photophysical properties, we introduce a 3,6 carbazole by electron deficient groups and electron rich groups benzoyl tert butyl TTM, and free radical reaction of two new TTM-1Cz Bz and TTM-1Czt B. free radical two free radicals exhibit high thermal stability (thermal decomposition temperature of 330 DEG C), the study found that TTM-1Cz Bz and TTM-1Czt B in n-hexane The emission peak of dodecane solution respectively in 614 nm and 640 nm, respectively, compared with TTM-1Cz nm and a blue shift of 14 12NM red shift in fluorescence quantum efficiency was 54% and 55%. respectively. The experimental results show that the lack of carbazole and light physical properties, introducing electron rich groups not only influence the free radical with light stability of free radicals the great influence. Compared with TTM-1Cz, TTM-1Cz light stability of Bz is reduced by 15 times, and the light stability of TTM-1Czt B is higher than TTM-1Cz more than 4.5 times. On the free radical component of single carrier mobility, electron deficient unit benzoyl radical makes the electron mobility increases, while the electron donating tert butyl lead device the hole and electron mobility decreased. In the end, we were prepared with two kinds of free radicals (TTM-1Cz Bz and TTM-1Czt B) as a light emitting object 5 wt.% doped in CBP OLED device, the maximum external quantum efficiency respectively. The peak wavelength of EL spectra of TTM-1Czt B doped devices in 5.2% and 2.8%. is 745 nm.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TN383.1;TQ422

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