【作者】 朱德喜；

【导师】 刘旭； 叶辉；

【作者基本信息】 浙江大学 ， 光学工程， 2009， 博士

【摘要】 聚合物电致发光器件由于在平板显示和照明领域的潜在应用前景,近年来成为国际众多研究机构和企业的研究热点。聚合物的偏振电致发光现象作为新兴的研究方向,其意义在于可作为液晶显示器的背光源,从而大幅提高光能利用率和简化元件结构。本研究工作以此为出发点,在传统聚合物电致发光器件的基础上,通过定向层的作用实现发光聚合物的取向排列,最终制备出具有偏振发光特性的聚合物电致发光器件。论文立足于发光聚合物薄膜器件,深入研究了偏振发光的理论基础、薄膜的光学各向异性表征和电致发光器件的制备,并在此基础上提出了新的定向层制作技术。1.论文从电磁辐射理论和聚合物液晶特性两个角度对聚合物偏振发光的物理机制进行论述。前者以偶极子振荡模型为理论依据,论证了聚合物发光的偏振态与分子主轴方向的一致关系;后者从分子结构的角度,证明了聚合物刚性棒状结构以及由此产生的液晶特性对偏振发光的决定性作用。有序参数是衡量薄膜取向程度的重要参量,从有序参数的定义出发推导出了薄膜二向色性表达式。2.由聚合物分子定向排列引起的光学各向异性是取向薄膜的重要光学特性。本文提出了一种基于聚合物材料色散模型,通过对反射和透过光谱的拟合确定薄膜光学常数(包括折射率和消光系数)和厚度的计算方法。利用单一反射光谱拟合,测定了聚合物电致发光器件中几种常用功能薄膜的光学常数。并采用不同偏振态的线偏振光作为测试光源,计算得到了三种发光聚合物取向薄膜的光学常数各向异性,其中PFBT和PFO-BT-DBT在峰值波长处的双折射率达到0.86和0.67。3.利用芴基聚合物的热致液晶特性,制备了具有显著偏振特性的红、绿、蓝单色和白光偏振电致发光器件。器件结构为ITO/Alignment layer/Active layer/Cathode,以机械摩擦空穴注入层PEDOT:PSS作为定向层。其中利用芴基发光聚合物PFO-BT-DBT链内生色团之间的能量转移,首次实现了单一聚合物白光偏振电致发光。通过测试发光聚合物的液晶相转变温度和取向薄膜的吸收和光致发光偏振光谱,确定了薄膜的最佳摩擦强度和热处理条件。在最佳取向条件下,器件电致发光偏振率高达24,为目前所报道的国际较高水平。器件同时具有良好的发光亮度和颜色稳定性,白光的CIE色坐标为(0.33,0.35),非常接近完美白光。4.为了避免机械摩擦定向层方法对器件发光带来的不利影响,开创性地采用了微压印技术制作定向层的表面微结构。采用热固化柔性硅橡胶PDMs作为印章,经微压印使PEDOT:PSS层形成了最小周期为1.6μm的光栅微结构。以此为定向层制备的发光取向薄膜同样具有显著的光学各向异性,而且光栅分辨率越高对取向越有利。更多还原

【Abstract】 Polymer light-emitting diodes(PLEDs) have been attracting much attention recently as a new technology for full-color displays and light sources.Polarized electroluminescence (EL) from polymer is researched in view of potential application as the backlight of liquid crystal display(LCD).The power efficiency of LCD will be significantly improved and the structure of device will be simplified if polarized PLEDs are employed.Based on the research of traditional PLEDs,polarized EL is realized from oriented light-emitting polymers on an alignment layer.With the main thread of the orientation of light-emitting polymer thin films,this thesis involves in the theory of polarized emission,the optical anisotropy characterization of oriented films and the devices fabrication,based on which a novel orientation technique is developed.1.The physical mechanism of polarized EL from polymers can be discussed through electromagnetic theory and liquid crystal state of polymers.The former demonstrates the consistency between the emission polarization and the direction of molecular backbone based on the dipole oscillation model.The latter indicates that the rigid rods structure plays a decisive role on the liquid crystal state of polymer,and therefore the polarized EL.An order parameter is introduced to character the orientation level of polymer films,from which the express of the dichroic ratio for oriented films is derived.2.The optical anisotropy caused by the aligned polymer molecular is an important characteristic for oriented films.Using the measured data of reflectance and transmittance, a photometric fitting method based on Forouhi-Bloomer dispersion model is developed to determine the anisotropic optical constants(including refractive index and extinction coefficient) and thickness of polymer thin films commonly.When the test incident light for spectra measurement is linearly polarized,the anisotropic optical constants of in-plane oriented polymer thin films can be determined.Oriented polymer films of three polyfluorene derivatives discussed in this thesis were measured.The calculated results indicate that PFBT and PFO-BT-DBT show the maximal birefringence of 0.86 and 0.67, respectively,at the peak wavelength.3.Four fluorene-based light-emitting polymers were used to fabricate polarized PLEDs of blue-,green-,red- and white-light emitting for their thermotropic liquid crystal characteristics.The device structure is ITO/Alignment layer/Active layer/Cathode,and the hole injecting layer poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate)(PEDOT: PSS) is mechanically rubbed as the alignment layer.Polarized white-light EL from a single copolymer poly(9,9-dioctylfluorene-4,7-bis(2-thienyl)-2,1,3-benzothiadiazole-2,1,3-benzo-thiadiazole) (PFO-BT-DBT) can be realized for the first time through intrachain energy transfer.The optimized rubbing strength and thermal treatment are employed,by measuring the phase transition temperatures as well as the polarized absorption and photoluminescence spectra of the oriented films.With the optimized thermal treatment,an EL polarized ratio of up to 24 was achieved,which is relatively high in the world.The PLED exhibits a good stability of efficient white emission with a CIE coordinate of(0.33, 0.35),which is almost the perfect white light.4.In order to avoid the effect on the device performance by the mechanically rubbed alignment layer,micro-imprint was employed.An thermal cured elastic polymer film of Polydimethylsiloxane(PDMS) served as the stamp,channels with a minimal period of 1.6μm were micro-imprinted on the PEDOT:PSS layer as the alignment layer.The light-emitting layer can also be oriented and shows obviously optical anisotropic by this method, which also indicates that a higher resolution of the microstructure helps to reach a more effective orientation.更多还原