Oct 4, 2018
Professor Xiangfeng Duan

The team reported on the development of a scalable and low-cost solution-based approach to making high-performance flexible TFTs and electronic circuits.

The study titled “Solution-processable 2D semiconductors for high-performance large-area electronics” was published online in the prestigious journal Nature on October 3, 2018. 

The research team was led by Duan, UCLA professor of chemistry and biochemistry, and Yu Huang, UCLA professor of materials science and engineering at the UCLA Samueli School of Engineering.

The lead author of the study is alumnus Dr. Zhaoyang Lin (Ph.D. ’16 chemistry, Duan Group), a postdoctoral researcher in the Duan group (pictured right). Other study authors are materials science and engineering postdoctoral researcher Dr. Yuan Liu (Ph.D. ’15 MSE, Huang Group), UCLA Chemistry & Biochemistry graduate students Yiliu Wang, Frank Song, and Chengzhang Wan, and researchers from University of Texas at Austin and Hunan University in China.

To learn more about the Duan group's research, visit their website.

About the Research (by Dr. Zhaoyang Lin)

Solution-processable large-area electronics from MoS2 2D nanosheets ink.
Image source: Duan Lab @UCLA Department of Chemistry & Biochemistry

Thin-film transistors (TFTs) are the fundamental building blocks for many large-area electronic applications, including the well-known TFT-LCD (a liquid-crystal display that uses TFT technology to improve image qualities such as addressability and contrast). In recent years, there has been a growing interest in flexible electronic visual display from numerous consumer electronics manufacturers (Sony, Samsung, LG, Apple, etc.), for the production of e-readers, mobile phones, electronic papers and other consumer electronics that are flexible and even wearable. It has, therefore, motivated considerable efforts in developing flexible TFTs that can retain proper functions in bent and even folded states. Additionally, for large-area electronic applications, the flexible TFTs should also be easily scalable for the cost-effective mass production.

This study reported a scalable and low-cost solution-based approach to fabricating high-performance flexible TFTs and electronic circuits, based on 2D semiconductor ink. The atomically-thin and intrinsically flexible 2D-nanosheets represent attractive building blocks for flexible/wearable electronics, similar to pieces of paper that can be easily bent, folded and flattened. However, the existing 2D-nanosheet inks usually exhibit very poor semiconductor behaviour, due to the non-uniformity of nanosheet thickness and defects generated in the nanosheet crystals during the ink formation processes. This new study introduces a new, mild molecular intercalation approach for effectively exfoliating bulk layered MoS2 crystals into highly uniform 2D nanosheets with little defects and thus well-preserved semiconductor properties. The TFTs produced from the resulting 2D-MoS2 nanosheet ink exhibit greatly improved device performance over existing solution-processed MoS2 TFTs, with at least one order of magnitude increase in carrier mobility and 3-4 orders of magnitude increase in switching ratio. Furthermore, the team has shown their approach is readily scalable with a high yield, for the first time allowing them to construct complex logic gates and computational circuits that were previously unattainable with other 2D inks.

The solution-phase fabrication process of these flexible TFTs is intrinsically scalable and cost-effective and can be readily made into the large scale (> m2) when combined with industrial roll-to-roll productions. In principle, it could dramatically reduce the cost to fabricate flexible displays on the next-generation TVs, monitors, phones, e-readers, and so on.

In the next step, the team plans to extend their approach to other similar layered crystals with even better electronic properties, and also to further improve the device integration processes to further improve the device performance. At the same time, they are exploring new printing approaches with these newly formulated inks for the scalable production of TFTs at a lower cost.