Researchers from the University of Maryland found that intercalating (embedding) sodium ions in a reduced graphene oxide (rGO) network, printed with graphene oxide (GO) ink, can significantly improve its performance as a transparent conductor in displays, solar cells and electronic devices.

The scientists used cost-effective materials and production techniques to receive a highly scalable printed electronics system that produces relatively inexpensive and stable conductors. The team theorizes the increased stability is due to the natural oxidation of sodium along the edges of the printed networks which forms a barrier that prevents ion loss. Networks printed with the ink exhibit up to 79 percent optical transmittance and 311 Ohms per square of sheet resistance.

The process begins with the creation of specially formulated ink containing graphene oxide (GO), which is applied evenly to a thin glass substrate. The coated substrate is heated and dried to evaporate the ink solution, leaving a thin, semitransparent layer of GO behind. It is then subjected to a second heat treatment at 300 degrees Celsius, which converts the GO to reduced graphene oxide (RGO). The process is repeated up to six times. The team then uses a tiny blade to cut and scrape away excess RGO, leaving behind a layered network. After adding thin film electrodes, the scientists moved the device into a glovebox (a chamber with an inert atmosphere) where they are able to add electrolytes and intercalate the sodium ions without the risk of unwanted chemical reactions. As the ions are inserted into the space between each layer of RGO, the network becomes more transparent and more conductive.