Thursday, July 18, 2024

Researchers create transparent conductors without expensive rare-earth indium

Transparent conductors play a vital role in displays, solar cells, and emerging printed electronics. Indium tin oxide is used in more than 95% of global transparent conductors. It conducts electric current through a device, which is disrupted when a person swipes or taps a touch screen.

Now, researchers at Purdue University have developed transparent organic conductors from patent-pending polymers that achieve the same results and properties as traditional conductors made from rare-earth minerals but are less expensive and can be created from more plentiful reserves.

Touch screens are made of several layers, including a top layer of glass or plastic, conductive layers beneath it, and a circuit board that reads the signals sent by the conductive layer.

“When a user touches the screen, their finger creates a disruption in the electrical field generated by the conductive layer,” said Jianguo Mei, the Richard and Judith Wien Associate Professor of Chemistry. “This disruption is detected by the circuit board, which can then determine the location of the touch and interpret it as a command, such as opening an app or typing a message.”

Because indium tin oxide is transparent as a thin film, users can view images, text, and video through it.

“Indium, tin oxide films, are mechanically fragile, which makes them undesirable in roll-to-roll manufacturing,” Mei said. “Also, indium is a rare-earth mineral with scarce reserves; the U.S. Geological Survey said the U.S. was 100% reliant on indium imports in 2021. Because demand for ITO films is increasing, the price of indium has soared. This has led to the search for alternatives, including metal mesh, graphene, and earth-abundant metal oxides and organic conductors.”

Researchers have created a patent-pending polymer from carbon-based materials with a lower manufacturing cost and easier to manufacture into thin films than indium through solution-coating processing.

Mei said the performance of the new thin-film transparent conductors also rivals that of conductors made with indium tin oxide. The formed polymer ink can endure storage temperatures from −20 to 65 °C.

“The polymer ink is shelf-stable for months under ambient conditions, compared to commercially available PEDOT:PSS,” Mei said. “Our new transparent organic conductors exhibit low sheet resistance and high transmittance compared to any other solution processable transparent conductors. Also, it exhibits excellent durability under accelerated weathering tests.”

The next step to advance the innovation will be to continually improve the figure of merit of their organic conductor and develop ink formation for large-scale processing.

Journal reference:

  1. Zhifan Ke, Ashkan Abtahi, Jinhyo Hwang, Ke Chen, Jagrity Chaudhary, Inho Song, Kuluni Perera, Liyan You, Kyle N. Baustert, Kenneth R. Graham, and Jianguo Mei. Highly Conductive and Solution-Processable n-Doped Transparent Organic Conductor. Journal of the American Chemical Society, 2023; DOI: 10.1021/jacs.2c13051