P-型及N-型摻雜石墨烯電極在有機電子元件之應用

Abstract

石墨烯為由碳原子以sp2鍵結方式形成的單原子層二維材料，在近年來受到廣大的討論及研究，因為石墨烯於電性、機械性質及熱導性質上都有特殊的表現。在我的研究中，我著重於將石墨烯優異的電性應用在有機電子元件上的導電電極上，由於純石墨烯具有雙載子傳輸特性，故對其摻雜使之成為P-型或N-型的材料是可行的，這也讓石墨烯電極有更多的應用。 在概述之後本論文會先介紹石墨烯的轉印及圖樣製程，我們利用熱脫膠帶來轉印石墨烯，好處是可大面積轉印且為乾製程，轉印多次堆疊後即可得到透明導電電極應用於有機太陽能電池上；而圖樣製程則用來定義有機薄膜電晶體的通道面積，搭配熱脫膠轉印後可製成上電極的結構而不傷害下方的高分子。 以一般有機電子元件來說，常需要選擇不同的金屬或導電電極來匹配不同有機材料的能帶圖，但石墨烯具有可調變功函數的特性，故我們藉由摻雜來使石墨烯功函數改變以匹配有機材料的能帶結構。在我的研究中，P型摻雜是利用硝酸，摻雜過後應用在P3HT/PCBM 太陽能電池的正極和P3HT 薄膜電晶體的源極/汲極，本研究結果顯示用P型摻雜石墨烯電極的元件表現相較於一般常用的金電極來的好；而N摻雜物則是用之前實驗室發現對石墨烯有良好N型摻雜效果的TiOx並將N型摻雜石墨烯電極應用於C60薄膜電晶體的源極/汲極，雖然摻雜後石墨烯電極元件表現不如鋁電極但相較於純石墨烯電極還是有較好的效果。總結來說，摻雜的石墨烯電極在電子元件上的應用還是展現出很大的發展潛力。

Graphene is an atom-thick layer constructed by carbon atoms in honeycomb lattice. It has attracted a lot of research in recent years due to its unique electronic, mechanical and thermal properties. In my research, I focused on the applications of graphene’s outstanding electronic property- as conducting electrodes in organic electronics. Since intrinsic graphene demonstrates ambipolar transport behavior, doping graphene in either p-type or n-type becomes feasible and further enlarges applications of graphene electrodes. In this thesis, transfer and pattern processes of graphene were narrated at first. We used thermal release tape to transfer graphene, which is a dry process and able to transfer large-area graphene at a time. For organic photovoltaics (OPVs), multilayer graphene films were stack up to form transparent conducting electrodes. And for organic thin film transistors (OTFTs), pattern process was performed to define the channel of source/drain electrodes. The procedures were different depended on the structures of OTFTs and we proposed a dry transfer process that was harmless to the underlying polymer. In organic electronics, metals and other conducting electrodes are usually chosen for specific organic materials to match their band diagrams except for graphene. Tunable workfunction is one of graphene’s significant features. So here we doped transferred graphene to improve its conductivity and tune its work function to match the band diagrams of different organic electronics. HNO3 was used for p-type doping. And the doped graphene electrodes were applied in the anode of P3HT/PCBM solar cell as well as the source/drain electrodes in P3HT thin film transistors (TFTs). HNO3-doped graphene electrode showed better performance in P3HT TFTs compared to Au electrode, which is commonly used in p-channel TFTs. On the other hand, we used TiOx as n-dopant and employed the n-doped graphene electrodes in C60 TFTs. TiOx-doped graphene electrodes performed better than pristine graphene electrodes though still not as good as Al electrodes. All in all, tuning workfunction of graphene by either p-type or n-type doping did improve performances of graphene electrodes in organic electronics. Moreover, doped graphene electrodes showed great potential in replacing ITO and metals in organic electronics.