【作者】 刘辉；

【导师】 路萍；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2021， 博士

【摘要】 白光有机发光二极管（WOLEDs）因其高效率、低功耗、自发光、柔性等优点,在固态照明领域有着广阔的应用前景。荧光-磷光混合型WOLEDs,兼具荧光材料的低成本、稳定性和磷光材料的高效率的特点,被认为是最理想的白光器件结构。为了实现该类器件的大规模商业化应用,需要进一步通过材料创新和器件优化等方法简化器件结构、提升器件效率、降低效率滚降、提高白光品质。混合型WOLEDs中的关键因素是蓝色荧光材料。蓝光材料的性质例如三线态能级,固态发光效率会直接影响器件结构和性能。本论文以高固态发光效率蓝色荧光材料为研究对象,开展了荧光-磷光混合型WOLEDs的结构设计和性能研究,致力于在简单的器件结构中实现高效率、低滚降、高品质的白光发射。主要的工作如下:1.蓝色荧光分子在聚集态下通常会发生荧光淬灭和光谱红移,需要采用掺杂技术制备器件,使得蓝光OLEDs和WOLEDs的结构复杂化,并常伴随着较大的效率滚降。针对这些问题,我们在经典蓝光基团蒽的9,10位连接聚集诱导发光（AIE）基团四苯乙烯和具有扭曲构型的三苯胺基团,得到了AIE分子TPAATPE。它在非掺杂薄膜中的发光效率可达82%。其非掺杂器件实现了纯蓝光发射,色坐标为（0.15,0.16）,最大外量子效率为6.97%。进一步采用TPAATPE的非掺杂蓝光层,双极性的热活化延迟荧光（TADF）材料PTZ-B作为磷光染料的主体,得到结构相对简单的白光器件。当PTZ-B作为橙色磷光分子PO-01的主体时,双色白光器件实现了高效的暖白光发射,色坐标为（0.44,0.44）,最大功率效率和外量子效率达69.5 lm W^-1和25.2%。为了提高显色指数,通过使PTZ-B发挥红色磷光Ir（piq）₃主体和自身绿光发射的双重作用,得到了三色白光器件,其显色指数可达92,色坐标为（0.34,0.38）,最大外量子效率和功率效率达25.3%和47.3lm W^-1。该工作为利用具有低三线态能级的蓝色荧光材料,制备高显色指数的混合型WOLEDs提供了新的思路。2.具有高三线态能级的蓝光材料用于混合型白光器件时,不仅能够提供蓝光组分,还可以作为磷光染料的主体,从而简化器件结构。除了高的三线态能级外,蓝色荧光材料还需要具有高的荧光效率、双极性传输性质以及良好的磷光主体性能。我们选择了两个具有高固态发光效率的菲并咪唑衍生物PPPIS和PPIDPS作为混合型WOLEDs中蓝光发射的主体。PPPIS和PPIDPS具有相似的分子结构,但是硫的不同氧化态使两个分子表现出不同的光物理性质。PPPIS具有弱电荷转移激发态性质,表现为深蓝光发射,而PPIDPS由于硫的氧化使其电荷转移激发态性质明显增强,光谱红移到了天蓝光区域。以PPPIS为蓝光发射主体的WOLED表现出更好的器件效果,最大功率效率和外量子效率分别为80.1lm W^-1和27.2%。在亮度为1000 cd m^-2时,外量子效率仍然能够保持在22.1%。3.我们对同样具有弱电荷转移激发态性质的菲并咪唑-联苯（PPIM）分子的器件性能进行了系统的研究。PPIM的非掺杂蓝光器件能够实现7.8%的外量子效率,色坐标为（0.153,0.068）。当其作为磷光染料的主体时,绿、橙和红光磷光器件的最大外量子效率分别能达到23.5%、30.8%和22.4%。在此基础上,双色（蓝-橙）白光器件最高可以实现28.5%的外量子效率和82.8 lm W^-1的功率效率,并且在1000 cd m^-2的亮度时,器件的外量子效率和功率效率仍然能保持在27.9%和70.3 lm W^-1,效率几乎没有滚降。另外,通过在PPIM和PTZ-B层中低浓度掺杂红色磷光Ir（piq）₃,三色白光器件实现了93的显色指数和24.2%的外量子效率。最后,与模型化合物对比发现,在菲并咪唑-苯（PPI）横轴位置上增加苯环能够使分子具有弱电荷转移态性质,提高发光效率,改善器件性能。4.芘并咪唑衍生物的非掺杂器件具有高亮度、高效率、低滚降的特点,但是由于大的π共轭平面,其电致发光光谱往往表现为天蓝光发射。借鉴第四章的工作,我们同样在芘并咪唑-苯的横轴位置上增加苯环,得到了芘并咪唑-联苯（PPy IM）分子。它在非掺杂薄膜中发光效率可达73.3%。其非掺杂器件能实现纯蓝光发射,色坐标为（0.160,0.128）,最大外量子效率为7.6%,在5000 cd m^-2的高亮度时,外量子效率仍然能达到7.2%,表现出很低的效率滚降。通过采用PPy IM的非掺杂蓝光层,以及PPIM作为PO-01的主体,实现了高效率、低滚降的WOLEDs。器件外量子效率和功率效率的最大值分别为23.5%和51.5 lm W^-1。即使在5000 cd m^-2的高亮度时,外量子效率仍然能够达到21.2%,仅有8%的效率滚降。而且,双发光层器件表现出很稳定的暖白光发射,1000 cd m^-2亮度时的色坐标为（0.454,0.439）,在400 cd m^-2到10000 cd m^-2亮度范围内色坐标变化值只有（0.004,0.003）。更多还原

【Abstract】 White organic light-emitting diodes（WOLEDs）have been regarded as the most promising technology in next-generation solid-state lighting because of the advantages of high efficiency,low power consumption,self-illumination and flexibility.Fluorescent-phosphorescent hybrid WOLEDs,combining the merits of low cost and good stability of fluorescent materials and high efficiency of phosphorescent dyes,are considered to be the most ideal device structure for WOLEDs.In order to realize the large-scale commercial applications of hybrid WOLEDs,it is necessary to further simplify device structure,improve device efficiency,reduce efficiency roll-off and improve color quality via materials innovation and device structure optimization.The key factor in hybrid WOLEDs is the blue fluorescent materials.The properties of blue materials such as triplet state energy level and solid-state photoluminescent quantum efficiency（PLQY）have a crucial influence on the design of device structure and resulting performance.In this paper,we carried out the structure design and performance research of fluorescence-phosphorescence hybrid WOLEDs by adopting blue fluorescent materials with high solid luminescence efficiencies,aiming at achieving WOLEDs with simple device structure,high efficiency and low roll-off.The main works include the following four parts:1.Blue fluorescent emitters usually undergo fluorescence quenching and spectral red-shift in aggregate state and thus require doping technologies to fabricate OLEDs,which commonly results in complicated device structure of OLEDs and relatively large efficiency roll-offs.To solve these problems,tetraphenylethene（TPE）group with characteristic of aggregation-induced emission（AIE）and triphenylamine unit possessing twisted conformation are introduced on the central core of anthracene to obtain an AIE molecule TPAATPE.Its PLQY in thin film can reach 83%.The non-doped device using TPAATPE as the emitter achieves pure blue emission with Commission International de L’Eclairage（CIE）coordinates of（0.15,0.16）and the maximum external quantum efficiency（EQE）of 6.97%.Furthermore,by utilizing TPAATPE as the non-doped blue-emitting layer（EML）,and PTZ-B,a bipolar thermal activation delayed fluorescence（TADF）molecule,as the phosphor host,a series of hybrid WOLEDs with relatively simple device structures are successfully prepared.When PTZ-B acts as the host of the orange phosphor PO-01,two-color WOLED achieves high-efficiency warm white emission with CIE coordinates of（0.44,0.44）.The maximum forward-viewing power efficiency（PE）and EQE are 69.5 lm W^-1 and25.2%,respectively.In order to improve the color rendering index（CRI）,three-color（blue-green-red）WOLED is fabricated by utilizing PTZ-B as the green component as well as the host of red phosphor Ir（piq）₃,and achieves pure white emission with CIE coordinates of（0.34,0.38）,high CRI of 92,maximum EQE and PE value of 25.3%and47.3 lm W^-1,respectively.This work provides a new idea for the preparation of hybrid WOLEDs with high CRI value using blue fluorescent materials possessing low triplet energy levels.2.When blue fluorescent materials with high triplet energy levels are used in hybrid WOLEDs,they not only provide blue emitting component,but also act as the host of phosphorescent dyes,thus simplifying the device structure of WOLEDs.In this type of WOLEDs,except for high triplet energy levels,blue fluorescent materials with high PLQY,bipolar transporting properties and fine device performance as host materials for phosphorescent dyes are also required.In this chapter,two phenanthroimidazole derivatives with high solid-state luminescence efficiency,PPPIS and PPIDPS,are selected as the blue-emitting hosts in WOLEDs.PPPIS and PPIDPS have similar molecular structures but with the different oxidation state of sulfur atom,which provides them with various photophysical properties.PPPIS shows weak charge transfer excited state property and exhibits deep-blue emission.However,because of the oxidation of sulfur atom,the charge transfer excited state property of PPIDPS is significantly enhanced,and the spectrum is red-shifted to sky-blue region.The two colors WOLED using PPPIS as the host of phosphor PO-01 shows better device performance with the maximum PE and EQE of 80.1 lm W^-1 and 27.2%,respectively.At the luminance of 1000 cd m^-2,the EQE can still maintain 22.1%.3.In this chapter,the device performance of phenanthroimidazole-biphenyl（PPIM）molecule,which also possesses the weak charge transfer excited state property,is systematically investigated.The non-doped device achieves a maximum EQE of 7.8%with the CIE coordinates of（0.153,0.068）.When PPIM serves as the phosphor host,the maximum EQE of green,orange and red phosphorescent devices can reach 23.5%,30.8%and 22.4%,respectively.On this basis,two-color WOLED achieves the maximum EQE of 28.5%and maximum PE of 82.8 lm W^-1,and the EQE and PE can still maintain 27.9%and 70.3 lm W^-1 at the luminance of 1000 cd m^-2 with negligible efficiency roll-offs.In addition,by doping red phosphor Ir（piq）₃in PPIM and PTZ-B layer at low concentration,three-color WOLED achieves a high CRI value of 93 and the maximum EQE of 24.2%.Finally,compared with the model compound,the introduction of benzene ring at the axis of phenanthroimidazole-phenyl（PPI）entitles the resulting molecule with weak charge transfer state property,significantly improves the luminescence efficiency and device performance.4.In prior studies,pyrenoimidazole derivatives can be applied in non-doped OLEDs with the properties of high brightness,high efficiency and low roll-off.However,due to the largeπ-conjugated plane,pyrenoimidazole derivatives usually show sky-blue electroluminescence.According to the work in chapter 4,we also add a benzene ring at the horizontal axis of pyrenoimidazole-phenyl to obtain pyrenoimidazole-biphenyl（PPy IM）molecule,which has a high luminescence efficiency of 73.3%in thin film.The non-doped device achieves pure blue emission with the CIE coordinates of（0.160,0.128）and the maximum EQE is 7.6%.Under the high luminance of 5000 cd m^-2,the EQE can still reach 7.2%,showing a very low efficiency roll-off.By using PPy IM as the non-doped blue EML and PPIM as the host of phosphor PO-01,hybrid WOLED with high efficiency and low efficiency roll-off is realized.The maximum EQE and PE can reach 23.5%and 51.5 lm W^-1,respectively.Even at the high luminance of 5000 cd m^-2,the EQE can still reach 21.2%,and the EQE roll-off was only 8%.Moreover,the device exhibits very stable warm white emission with CIE coordinates of（0.454,0.439）at the luminance of 1000 cd m^-2,and the CIE coordinates variation is only（0.004,0.003）in the luminance range of 400 cd m^-2 to10000 cd m^-2.更多还原