标题: | 采用高折射率基板来提升发光电化学元件的光萃取量 Enhancing Extracted Electroluminescence from Light-Emitting Electrochemical Cells by Employing High-Refractive-Index Substrates |
作者: | 张雅棻 苏海清 Jang, Yea-Fen Su, Hai-Ching 光电系统研究所 |
关键字: | 光萃取;波导模态;有机发光电化学元件;基板模态;light extraction;waveguide mode;light-emitting electrochemical cells;substrate mode |
公开日期: | 2017 |
摘要: | 固态发光电化学元件(light-emitting electrochemical cells, LECs)和传统有机发光元件(organic light-emitting devices, OLEDs)相比有许多优点,例如元件结构简单可以使用溶液制程来制作元件,低操作电压和可以使用惰性金属作为阴极等优势。然而发光电化学元件的效率仍有改善空间,例如提升光萃取量以满足实际应用的要求。在所有被局限在发光电化学元件的光学模态中,局限在基板模态的光是最容易被萃取出来的,例如藉由简单的将基板的出光表面磨雾,便可以萃取出基板模态中的光。因此增加基板模态的比例对于提升光萃取量是非常有效的方式。在此实验中分析藉由应用不同折射率的材料作为基板时,发光电化学元件中光学模态比例的变化。当使用高折射率材料作为基板时,会有更多的光被局限在基板模态中。此外,当基板与铟锡氧化物(indium tin oxide, ITO)层之间的折射率差异越小,可以让被铟锡氧化物薄膜层局限的光(波导模态),其达到截止条件的波长范围扩大。而减少铟锡氧化物薄膜层中波导模态的比例也有助于将光自发光电化学元件中萃取出来,因为将光从波导模态中耦合出来需要更复杂的技术才能达成目的。因此本实验使用可以从市面上购买到的未抛光蓝宝石当作基板制作元件,其元件的出光量和以玻璃为基板制作的元件相比提升了56%,而在铟锡氧化物薄膜层和蓝宝石基板之间加入一层散射层,可以从基板模态中萃取更多的光,并使出光量提升71%,而藉由使用钌错合物作为发光电化学元件的发光层材料可以使外部量子效率高达5.5%,此元件效率在现有的红光电化学元件研究论文中是很高的值,证实了利用高折射率材料作为基板来提升发光电化学元件的出光量是一个既简单又有效的方法。 Solid-state light-emitting electrochemical cells (LECs) show several advantages over conventional organic light-emitting devices (OLEDs) such as simple device structure compatible with solution processes, low operation voltage and capability of utilizing inert cathode metals. However, device performance of LECs must be improved, e.g. enhancing light extraction, to meet the requirements for practical applications. Among the optical modes trapped in LECs, light trapped in substrate mode is easier to be extracted, e.g., by simply roughing the output surface. Therefore, increasing the percentage of substrate mode is beneficial in improving light extraction. In this work, the contributions of optical modes in LECs employing substrates with various refractive indices are analyzed. Higher-refractive-index substrates are shown to trap more light in the substrates. Furthermore, smaller refractive index difference between substrate and indium tin oxide (ITO) layer increases the cutoff spectral range of light waveguided in ITO layer. Reducing the percentage of waveguide mode in ITO layer also facilitates light extraction since it requires more complicated methods for outcoupling light in waveguide mode. With commercially available unpolished sapphire substrates, light output of LECs is enhanced by 56%. When a scattering layer was inserted between ITO and sapphire substrate, more light in substrate mode can be extracted and 71% enhancement in light output is realized. High external quantum efficiency up to 5.5% is consequently obtained in LECs based on a ruthenium complex. Such device efficiency is among the highest reported values for red-emitting LECs and thus confirms that utilizing higher-refractive-index substrates would offer a simple and feasible approach to improve light output of LECs. |
URI: | http://etd.lib.nctu.edu.tw/cdrfb3/record/nctu/#GT070458005 http://hdl.handle.net/11536/140923 |
显示于类别: | Thesis |