Spray-on clear coatings for cheaper smart windows

A simple method for making clear coatings that can block heat and conduct electricity could radically cut the cost of energy-saving smart windows and heat-repelling glass.

The spray-on coatings developed by researchers at RMIT University are ultra-thin, cost-effective and rival the performance of current industry standards for transparent electrodes.

GALLERY  

Combining the best properties of both glass and metals in a single component, a transparent electrode is a highly conductive clear coating that allows visible light through.

The coating is a key component in technologies, including smart windows, touchscreen displays, LED lighting, and solar panels. However, the current manufacturing of these clear coatings is made through time-consuming processes that rely on expensive raw materials.

The newly developed spray-on method is fast and based on cheaper materials that are readily available. The technique could simplify the fabrication of smart windows, which can be both energy-saving and dimmable, as well as low-emissivity glass, differing to conventional glass panels which only focus on blocking out UV-light. The spray coater process can be automatically controlled and programmed, meaning that this new technology is scalable. Fabricating bigger proof-of-concept panels will be relatively simple.

Lead investigator Dr Enrico Della Gaspera said the pioneering approach could be used to substantially bring down the cost of energy-saving windows and potentially make them a standard part of new builds and retrofits.“Smart windows and low-E glass can help regulate temperatures inside a building, delivering major environmental benefits and financial savings, but they remain expensive and challenging to manufacture,” said Della Gaspera, a senior lecturer and Australian Research Council DECRA Fellow at RMIT. “The ultimate aim is to make smart windows much more widely accessible, cutting energy costs and reducing the carbon footprint of new and retrofitted buildings.”

How the tech works

In the new study published in the journal Advanced Materials Interfaces, researchers in RMIT’s School of Science made transparent electrodes using the far cheaper material tin oxide, spiked with a unique combination of chemicals to enhance conductivity and transparency. The ultra-thin transparent coatings, which are over 100 times thinner than a human hair, only allow visible light through, while blocking both harmful UV light and heat in the form of infrared radiation.

The scientists used a process called “ultrasonic spray pyrolysis” to fabricate smooth, uniform coatings of high optical and electrical quality. A precursor solution is nebulised, using commercially available technology to create a fine spray mist that forms ultra-small and uniformly-sized droplets. This solution is sprayed on a heated support layer, such as glass.  When the solution hits the thermal layer, a chemical reaction is triggered, decomposing the precursor into a solid residue that is deposited as an ultra-thin coating. All the by-products of this chemical reaction are eliminated as vapours, leaving a transparent layer with the desired composition.

Global demand for smart glazing

The global market size for smart glass and smart windows is expected to reach $6.9 billion by 2022, while the global low-E glass market is set to reach an estimated $39.4 billion by 2024. New York’s Empire State Building reported energy savings of $US2.4 million and cut carbon emissions by 4,000 metric tonnes after installing smart glass windows.

Eureka Tower in Melbourne features a dramatic use of smart glass in its “Edge” tourist attraction, a glass cube that projects 3m out of the building and suspends visitors 300m over the city. The glass is opaque as the cube moves out over the edge of the building and becomes clear once fully extended.

The research was supported through funding from the Australian Research Council, with crucial imaging and analysis conducted at RMIT’s Microscopy and Microanalysis Facility (RMMF). The work was enabled in part by use of the Central Analytical Research Facility (CARF) at the QUT Institute for Future Environments.

‘Ultrasonic Spray Pyrolysis of Antimony-Doped Tin Oxide Transparent Conductive Coatings’, with collaborators from La Trobe University and Queensland University of Technology, is published in Advanced Materials Interfaces (DOI: 10.1002/admi.202000655). 

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