P-型及N-型摻雜石墨烯電極在有機電子元件之應用

Abstract

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.