全噴墨有機半導體摻雜石墨烯之薄膜電晶體效能提升研究

Abstract

近年來由於消費者對資訊產品便利性以及易於攜帶的需求，市場對軟性電子的期待逐漸提高，使得一些原本使用無機材料所製作的電子產品逐漸使用有機材料來製作以達到可撓的效果，例如可撓式顯示器、太陽能電池、電子紙及RFID標籤等，其中有機薄膜電晶體更是被廣泛的應用於顯示器的背板。 有機材料通常使用溶液製程，具有成本低以及低溫製程的優勢，但其電性表現往往不如無機材料，目前有機薄膜電晶體受限於其電性，只能被應用於較低階的電子產品，如何提升有機材料的電性表現便成為一個重要的課題。 本論文使用團隊自行架設的噴墨系統與學長所建立的噴墨製程SOP，利用全噴墨製程搭配全有機材料，並透過在半導體材料P3HT中摻雜石墨烯製作出電性提升的有機薄膜電晶體；在摻雜濃度Graphene/P3HT = 2 wt.% 時的載子漂移率為Pristine P3HT的十倍，且電流開關比大於105，同時也找出石墨烯摻雜P3HT在逾滲理論中的臨界值，並探討摻雜石墨烯後接觸電阻與通道電阻的改變。 另外，本論文透過X光粉末繞射儀、傅立葉轉紅外線光譜儀來觀察摻雜石墨烯後P3HT的晶格狀態以及分子內部是否有產生新的官能基及鍵結，以及透過紫外光/可見光光譜儀及螢光光譜儀來探討電子在石墨烯與P3HT中的行為，證實兩者之間確實有電荷轉移的現象存在，石墨烯在P3HT半導體層中扮演載子移動時的優先路徑，可提升電晶體的電性。

In recent years, information terminal devices have become more convenient and easily portable to meet customers’ needs. This desire and request gradually stimulates the development of flexible electronics. Electronic products made of inorganic materials in the past are replaced by organic materials in order to achieve the goal of being” flexible”, such as flexible display, solar cells, electronic paper and RFID tags. In the fabrication process of organic devices, solution based process were adopted in this study, which have advantages such as low cost and low process temperature. However, the performance of state of the art organic thin film transistors (OTFT) are usually poor compare with thin-film transistor made of inorganic materials. The performance improvement on OTFT is therefore an important research issue and will be investigated in this thesis. In this study, the system set up by our research team and the OTFT standard operation process (SOP) developed in house is adopted, which is already proven to be a stable all ink-jet printing process. To improve the performance of all organic thin-film transistors, we blended graphene into P3HT. At blending concentration 2 wt.%, the mobility was ten times higher than pristine P3HT, while keeping the On/Off Ratio larger than 105. We also observed the decrease of contact resistance and channel resistance in our experiment. Furthermore, we found the percolation limit of blended graphene in P3HT. To understand the charge behavior in P3HT and graphene, material analyses such as XRD, FTIR, UV-Vis and PL are conducted to observe the lattice state, molecular internal vibration, and charge behavior after blending graphene with P3HT, respectively. These analyses demonstrated that the performance of the transistors can be improved since charge transfer between P3HT and graphene indeed exists and graphene sheets act as a preferential path which caused charge transport more easily than in pristine P3HT.