Crystally PBTTT-based OFET drived under low voltage

Po-Hsiang Fang^1*, Yi-Chen Tien¹, Fu-Chiao Wu¹, Horng-Long Cheng¹, Wei-Yang Chou¹

¹Department of Photonic, National Cheng Kung University, Tainan, Taiwan

* Presenter:Po-Hsiang Fang, email:l78011130@mail.ncku.edu.tw

Recently, the conjugated polymer material PBTTT-C14 has received many attentions because it can form extended crystalline domains from the liquid crystal phase at a specific temperature. The ordered arrangement between adjacent alkyl chains contributes to the crystallinity and tightly packed layered structure of PBTTT-C14, facilitating carrier transport and increasing carrier mobility. In this study, PBTTT-C14 films were fabricated using two different process methods, including spin-coating and thermal gradient epitaxy. The organic polymer material commonly contains impurities, thus affecting the electrical characteristics of the PBTTT-C14-based devices made by spin-coating. In the thermal gradient epitaxial process, PBTTT-C14 was blended with HMB and the PBTTT-C14 liquid crystal phase could crystallize in a specific direction to form an ordered microstructure with the aid of HMB crystallization. Meanwhile, HMB could eliminate the impurities in PBTTT-C14. The electrical characteristics of the PBTTT-C14-based devices from the thermal gradient epitaxial process were improved significantly compared to those from the spin-coating process. The on/off ratio and carrier mobility of the devices fabricated by spin-coating were 10¹ and 0.006 cm²/Vs, respectively, and those by the thermal gradient epitaxial process were 10³ and 0.06 cm²/Vs, respectively. Atomic force microscopy (AFM) was used to analyze the surface of the PBTTT-C14 thin films made by the two different process methods. There are many holes existing at the surface of the thin films from the spin-coating process, while the surface of the thin films from the thermal gradient epitaxial process shows an obvious crystalline line. This result verifies that the electrical characteristics of the PBTTT-C14-based devices fabricated by the thermal gradient epitaxial process are better than those made by the spin-coating process.

Keywords: conjugated polymer , low voltage, Crystally