Plasma Coating Offers Cost-effective, Sustainable Alternative to Indium

Researchers from the University of Sydney have developed a low-cost, sustainable, and readily available technology that can dim the screens of electronic devices, antireflection automobile mirrors, and smart architectural windows at a fraction of the cost of current technology. Created via a plasma sputtering process, the team’s technology is more accessible than indium, the rare-earth element currently used to provide smart devices with dimming capabilities. Like indium, the team’s plasma-generated structures are optically transparent, electrically conductive, and electrochromic.

The dielectric/material/dielectric (DMD) structures are composed of tungsten oxide (WO₃) and silver (Ag). The structures have three layers: Ag-doped WO₃, Ag, and WO₃. The WO₃ and Ag “sandwich” is coated onto glass.

Using high-power impulse magnetron sputtering (HiPIMS), the researchers deposited the WO₃ and the Ag/WO₃ layers. The nanocomposite structure was formed when high rates of Ag ionization occurred in the HiPIMS process and affected the negatively biased DMD structures enough to penetrate into the external WO₃ layer.

The new electrochromic material is created using a process called plasma sputtering. Courtesy of Behnam Akhavan.

The team optimized the surface plasmon resonance effect by changing the size of the silver nanoclusters through vacuum post-annealing in the same sputtering chamber, at varied temperatures. The optimized structure was transparent and electrically conductive. It demonstrated electrochromic characteristics with high coloration efficiency, fast switching speed, and long-term stability.

The plasma-generated material can be used to coat almost any solid surface, including flexible plastics, electronic papers, smartphones, and glass windows. It can be dimmed by applying a small electrical current, and the opacity can be changed by varying the voltage.

Indium, the material traditionally used to achieve optical transparency and electrical conductivity, has been put to wide use in smart devices. However, future supplies of this scarce rare-earth metal, which is mined as a byproduct of zinc, are uncertain.

Behnam Akhavan led the group that developed the plasma-generated, hybrid material that offers a low-cost, accessible, and environmentally sound alternative to using indium for dimming windows and computer screens.

The researchers believe that their plasma-based approach to fabricating transparent-conductive nanocomposite coatings on indium-free substrates has significant potential for the manufacturers of next-generation optoelectronic materials such as electrochromic devices.

The layered nanotechnology of the plasma-engineered material developed by the University of Sydney research team. Courtesy of Behnam Akhavan.

“When you change the transparency of a wearable electronic or a smart window, an electrochromic device is doing the work,” Akhavan said. “Until now, these devices have typically relied on materials like rare indium to do the job. What we have created is a manufacturer’s dream — a technology that removes the need for indium and instead uses a plasma-engineered, three-layered structure that is much cheaper to produce.”

The research was published in Solar Energy Materials and Solar Cells (www.doi.org/10.1016/j.solmat.2021.111268).