Liquid Crystals and Polymers in Application of Opto-Electronic Devices

本論文旨在探討新穎材料於光電元件上的製作與應用，此類對光有特殊作用的材料包括光聚合高分子與具導電性的共軛高分子。在此研究中，我們成功地使用液晶與高分子混合物，並藉由相分離方式製做出微透鏡陣列。此外，近幾年綠能源逐漸成為大家關注的議題，我們也嘗試使用軟壓印方法與摩擦配向技術應用於有機太陽能電池元件，除改善與簡化煩瑣的製作過程，並達成提升效率與其光電物理性質。 在微透鏡陣列的主題中，使用常溫下紫外光聚合方式引誘液晶/光聚合分子相分離的過程製做出自我組裝的微透鏡陣列。由於液晶與光聚合分子對於紫外光有不同的吸收能力，藉由光罩的輔助結果下，光聚合分子在曝光處硬化；同時，液晶則被推擠在遮光處，因而形成相分離的柱狀結構。之後，藉由破壞柱狀結構而產生表面張力不一致的區域，因表面張力差異性驅使未聚合完全的光聚合分子移動，且聚集自我組裝形成凸透鏡的陣列。此方式製做的微透鏡陣列不只整齊均勻且有效地呈現聚光能力，並期可運用在太陽能電池或發光二極體元件。 在太陽能電池方面我們採用常見的塊材異質接面(bulk heterojunction)主動層材料P3HT與PCBM製作元件。第一部分則採用軟壓印法將自組裝單分子層材料(CF3-silane)改質電極表面，使之成為太陽能元件中的電子阻絕層(EBL)。從研究結果可知，與一般常使用的PEDOT:PSS相較之下，CF3-silane擁有較高的功函數並與主動層材料的HOMO相近，此外因為單分子薄膜不僅透光度佳，且具有修飾ITO玻璃表面缺陷的作用；甚而，因為CF3 分子的疏水性質，可以改善主動層成膜的特性並輔助電子施體與電子受體材料之間相分離。第二部分，引入液晶面板界廣泛使用摩擦配向技術來製作有機太陽能電池元件。利用此簡單的技術在PEDOT:PSS表面快速地產生奈米級溝槽，並有效地增加主動層的光吸收率。此外，由於溝槽的表面形態有利於激子分離後，以確保電荷傳輸至電極並減少再結合現象發生。研究結果顯示，用具有奈米溝槽的PEDOT:PSS可以增加與主動層之間的接觸面積，並讓元件的光電轉換效率從原先的3.45%提升至3.82%。Novel materials, liquid crystals, photopolymers and conducting polymers, have many significant applications in micro optics, organic photovoltaic (OPV) cells and liquid crystal displays (LCD) manufacturing. In this dissertation, we successfully fabricate polymer microlens arrays and polymer solar cell devices by using these materials and investigate the electric, optical and physical properties to characterize their several advantages and vantages in the future position for optoelectronic devices. At first, a low-temperature self-assembly method using phase separation is demonstrated for the first time to fabricate polymer microlens arrays. In this study, we present a simple method of producing microlens arrays based on liquid crystal/photopolymer blends phase separation. The morphology of the microlens arrays has been measured by SEM, AFM and scanning white light interferometer. Our results show that the microlens arrays obtained from our experiments have a comparable light-gathering capability and can be applied in optical systems. In the latter, there are two topics concerning polymer solar cells. The first one is “Self-Assembled Multilayers Modified ITO in Polymer Solar Cells by Soft-Imprinting”. In this work, surface modification of indium tin oxide (ITO)-coated substrates through the use of self-assembled multilayers by the soft-imprinting method has been applied to adjust the anode work function and device performance in polymer solar cells based on a P3HT:PCBM heterojunction. The efficiency and morphology of the solar device with CF3-terminal group materials as a buffer layer have been measured and investigated. These results demonstrate that the soft-imprinting method is an effective and rapid procedure that enhances the quality of polymer solar cells and indicates potential implications for other organic devices containing an interface between a blended organic active layer and an electrode layer. In the second topic, we represent a fascinating approach – the rubbing method – to produce periodic grooves of PEDOT:PSS layer and apply it in polymer solar cells based on a P3HT:PCBM heterojunction. The 500 nm wide and 10 nm deep grating-like features have a profound effect on carrier mobility, light trapping and hole collection efficiency, leading to an increase in the short circuit density, filling factor and power conversion efficiency. These results indicate the feasibility of the rubbing method which is applicable to high-efficiency OPV cells