【作者】 李远；

【导师】 曹镛； 朱旭辉；

【作者基本信息】 华南理工大学 ， 材料学， 2010， 博士

【摘要】 近年来,对于溶液加工分子型有机光电材料的研究日益受到重视。一方面,可溶性有机分子光电材料通常情况下可用常规有机分离纯化方法,得到高纯度样品,从而可给出较为明确的分子结构-光电性能关系,为进一步分子、器件设计提供了可靠的依据。另外一方面,相对于依赖“真空蒸镀”成膜的有机分子材料,溶液加工分子型有机光电材料可降低器件制作成本、适合于制备大面积光电器件。在本论文中,我们围绕高性能可溶液加工的非掺杂电致绿光材料展开研究。在分子设计上,着重提高材料的溶解性、可成膜性、薄膜形貌稳定性、电子注入/传输特性、光致、电致光谱色纯度以及光致、电致发光效率。对于电致发光材料,非对称结构的分子设计可以较好的防止分子聚集态的形成,提高发光效率。我们首次合成了以2,1,3-苯并噻二唑为核、不对称结构的绿光小分子化合物,命名为1a和1b。这两个化合物以2,1,3-苯并噻二唑为核,在其4,7-位分别引入咔唑的衍生物和烷氧基取代的苯基树枝。结构为:ITO/PEDOT:PSS(50 nm)/PVK(40nm)/1a(45 nm)/Ba (4 nm)/Al(120 nm)的电致发光器件表现出电流效率为10.6 cd/A的高效绿光发射,色坐标为(0.34, 0.58),比较接近纯绿光发射。基于以上工作,我们发现:化合物1a和1b在引入PVK的双层器件在高电流密度下,器件效率会显著下降。为了深入理解材料的电荷传输性质,我们在2,1,3-苯并噻二唑的4-位和7-位对称引入了咔唑和芴的衍生物基团,合成了化合物1c和1d,并将化合物1c和第二章的两个化合物1a和1b进行器件表征方面的比较研究。器件结构为ITO/PEDOT:PSS (50 nm)/1a(1b, 1c, 45 nm)/TPBI (30 nm)/LiF (2 nm)/Al (120 nm)的电致发光器件,进一步提高了器件的性能,化合物1a的最大电流效率为12.8 cd/A的高效绿光发射。该材料在增加了电子传输层的电致发光器件中,在高电流密度下电流效率下降较为平缓,在电流密度为20 mA/cm2的时候,电流效率依然有11.2 cd/A,最大亮度达到29271 cd/cm2。为了简化合成,我们采用了结构简单且易形成非晶态的结构单元咔唑的衍生物和1,3-双(1-萘)基苯,合成了两个以2,1,3-苯并噻二唑为核的玻璃态小分子材料CzFBTB和NBBTB。分子一端的刚性树枝赋予了材料的内在稳定的玻璃态性质,另一端增溶性的烷氧基取代的苯基树枝使得材料具有较好的溶解性。以CzFBTB为活性层的电致发光器件ITO/PEDOT:PSS (50 nm)/PVK (40 nm)/CzFBTB (45 nm)/Ba (4 nm)/Al (120 nm)电流效率达3.5 cd/A。在保证材料的空穴注入性能和成膜性的前提下,我们引入了4,7-二苯基-2,1,3-苯并噻二唑作为核,合成了不对称取代的4,7-二苯基-2,1,3-苯并噻二唑的衍生物NCFPBT,该化合物在电致发光器件中获得了比较好的器件效率和色纯度。在器件结构:ITO/PEDOT: PSS (50 nm)/PVK (40 nm)/NCFPBT(45 nm)/CsF (2 nm)/Al (120 nm)中,在未优化的情况下,化合物NCFPBT即表现出7.66 cd/A的最大电流效率,电致发光光谱的半峰宽相对减小,相对于第二章的两个化合物1a和1b的色坐标为(0.34, 0.59)。更进一步改进材料的电子注入/传输特性,我们设计并合成了含有二苯基磷氧键取代噻吩为端基,2,1,3-苯并噻二唑为核的发光材料,该化合物发光颜色为黄绿光。缺电子的二苯基磷氧基团使该材料具有比较好的电子注入性质,同时具有较高的光致发光效率。我们对化合物的合成、表征和光物理性质进行了初步的探索,器件表征正在进一步研究。更多还原

【Abstract】 Solution-processable molecular semiconductors have received increasing attention. Withrespect to their polymer counterparts, small molecular active compounds present theadvantages of a monodisperse unequivocal chemical structure and thus of a potentially betterreproducibility of synthesis and purification and more straightforward analysis ofstructurep?roperties relation-ships. Furthermore, when adequately solubilized by design thesesolution-processable molecular materials afford the possibility of low-cost large areaelectronics with respect to vacuum deposition-based device processing techlelogy.The research of this thesis has focused on the design, preparation and characterization ofnew efficient non-doped solution-processible green light-emitting molecular materials. Theemphases of molecular designs have been placed on the issues such as solution solubility,film-forming property, morphological stability, electron injection and transport,photoluminescent and electroluminescent efficiency and emission color purity.For the molecule design of electroluminescent materials, non-symmetrical moleculestructure may prevent the formation of molecular aggregation state thus increasingluminescent efficiency. We first synthesized a series of green light-emitting compoundswhich were named as 1a and 1b, based on an asymmetrically 4,7-disubstituted2,1,3-benzothiadiazole. The building block containing the derivative of carbazole wasintroduced on the 4-position of the core 2,1,3-benzothiadiazole core, while the alkoxysubstituted phenyl dendritic block was introduced on the 7-position of 2,1,3-benzothiadiazole.The devices with structure of ITO/PEDOT: PSS (50 nm)/PVK (40 nm)/1a (45 nm)/Ba (4nm)/Al (120 nm) exhibited a current efficiency of 10.6 cd/A. The color coordinates of thehigh-performance green emission were (0.34, 0.58) which were very close to pure greenemission.Based on the above results, it was noticed that the efficiencies of compounds 1a and 1bdecreased significantly in in double-layer devices with PVK at high current density. In orderto understand the properties of charge transport, we synthesised compounds 1c and 1dthrough introducing the derivative of carbazole and alkylfluorene at both the 4-position and7-positin of the core 2,1,3-benzothiadiazole. In comparison with compounds 1a and 1b inChapter 2, we prepared the similar device characterizations in the device structure:ITO/PEDOT: PSS (50 nm)/1a (1b, 1c, 45 nm)/TPBI (AlQ3, 30 nm)/LiF (2 nm) /Al (120 nm).We improved the performance of the devices. Compound 1a showed a high current efficiencyof 12.8 cd/A while the electron transport layer TPBI was introduced in the electroluminescent devices. The efficiency roll-off was improved and the efficiency decreased more slowly athigh current density. The current efficiency still maintained on a level of 11.2 cd/A at acurrent density of 20 mA/cm2. The maximum brightness of all devices reached 29271 cd/cm2.To simplify the synthesis, we synthesised two small molecular emitters CzFBTB andNBBTB with the derivative of carbazole and 1,3-di(naphthalen-1-yl)benzene which bear asimple structure and trend to form amorphous film. The two molecules with 2,1,3 -benzothiadiazole core exhibited intrinsicly amorphous glass state owing to the rigidmolecular dendrons at one end of molecule. The solubility of compounds was ensured bysolubilized diphenylphenyl moiety at the other end of molecule. The electroluminescentdevice ITO/PEDOT: PSS (50 nm)/PVK (40 nm)/CzFBTB (45 nm)/Ba (4 nm)/Al (120 nm)showed a current efficiency of 3.5 cd/A.A new asymmetrically substituted green emitter NCFPBT was prepared by theintroduction of the core 4,7-diphenyl-2,1,3-benzothiadiazole, which preserved hole injectionability and the film-forming property of material. The compounds obtained a relatively bettercolor purity and efficiency in electroluminescent devices. In the device structure: ITO/PEDOT: PSS (50 nm)/PVK (40 nm)/NCFPBT (45 nm)/CsF (2 nm)/Al (120 nm), thecompound NCFPBT exhibited a maximum current efficiency of 7.66 cd/A withoutoptimization of devices. The half peak width of electroluminescence spectra was relativelysmaller than compounds 1a and 1b in Chapter 2 and the color coordinates were (0.34, 0.59).For further enhancement electron injection/transport properties, we designed andsynthesized a yellow-green light-emitting compound in which diphosphine oxide groupsubstituted at thiophene as terminal group at both sides of the core 2,1,3-benzothiadiazole.The electron-deficient functional diphosphine oxide groups may endow the material withgood electron injection and transport properties and high photoluminescence efficiency. Apreliminary exploration of the synthesis, characterization and photophysical properties of thenew compound were done. The device characterizations are currently underway in ourlaboratory.更多还原