Daowei He1,*, Jingsi Qiao2,3,*, Linglong Zhang1, Junya Wang1,4, Tu Lan1, Jun Qian1, Yun Li1, Yi Shi1,†, Yang Chai3, Wei Lan4, Luis K. Ono5, Yabing Qi5, Jian-Bin Xu6, Wei Ji2,7,† and Xinran Wang1,†
1National Laboratory of Solid State Microstructures, School of Electronic Science and Engineering, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
2Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing 100872, China.
3Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, P.R. China.
4School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China.
5Energy Materials and Surface Sciences Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Kunigami-gun, Onna-son, Okinawa 904-0495, Japan.
6Department of Electronic Engineering and Materials Science and Technology Research Center, The Chinese University of Hong Kong, Hong Kong SAR, China.
7Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China.
†Corresponding author. Email: firstname.lastname@example.org (X.W.); email@example.com (Y.S.); firstname.lastname@example.org (W.J.)
* These authors contributed equally to this work.
DOI:10.1126/sciadv.1701186 Publication Date: Sept. 6th 2017
Organic thin-film transistors (OTFTs) with high mobility and low contact resistance have been actively pursued as building blocks for low-cost organic electronics. In conventional solution-processed or vacuum-deposited OTFTs, due to interfacial defects and traps, the organic film has to reach a certain thickness for efficient charge transport. Using an ultimate monolayer of 2,7-dioctylbenzothieno[3,2-b]benzothiophene (C8-BTBT) molecules as an OTFT channel, we demonstrate remarkable electrical characteristics, including intrinsic hole mobility over 30 cm2/Vs, Ohmic contact with 100 Ω · cm resistance, and band-like transport down to 150 K. Compared to conventional OTFTs, the main advantage of a monolayer channel is the direct, nondisruptive contact between the charge transport layer and metal leads, a feature that is vital for achieving low contact resistance and current saturation voltage. On the other hand, bilayer and thicker C8-BTBT OTFTs exhibit strong Schottky contact and much higher contact resistance but can be improved by inserting a doped graphene buffer layer. Our results suggest that highly crystalline molecular monolayers are promising form factors to build high-performance OTFTs and investigate device physics. They also allow us to precisely model how the molecular packing changes the transport and contact properties.