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Researchers in China have fabricated transparent and flexible LED screens using a simple, low-cost manufacturing process based on silver nanowires. Liu Yang and colleagues at Zhejiang University say their technique is an improvement on existing screens, which are too opaque for some applications and can be brittle when deposited on flexible substrates. Their technology could soon bring diverse new capabilities to displays built into the walls and windows of modern buildings.

In recent years, transparent LED screens have become a focus of efforts to make flexible video displays using substrates like glass and clear plastic. Such screens are made from networks of highly transparent conductive circuits that connect their constituent LEDs together. For screens measuring a metre or more, either fluorine-doped tin oxide or indium tin oxide are typically used to construct the circuits. However, networks of this type suffer from several shortcomings, including a complex and expensive manufacturing processes as well as brittleness and a lack of transparency.

In order to design an effective alternative, Yang’s team needed to fabricate a network of wires that was dense enough to distribute electric current throughout the screen, but also sparse enough to preserve transparency. This led them to silver nanowires, which have excellent optical transmittance, electrical conductance, and mechanical flexibility. To manufacture their nanowires, Yang and colleagues first coated plastic and glass substrates with sacrificial masks, etched with networks of straight lines. After treatment in a specialized solution, these lines became stickier than the rest of the substrates. A further spray-coating process led to silver nanowires forming only along these sticky lines, creating an intricate network.

Using this technique, the researchers fabricated a series of 25cm-long, transparent and highly uniform conductive strips from both types of substrate. Through experiments, they showed that these strips possessed both high optical conductivity and low resistance, making them superior to previous tin oxide-based materials. In addition, they demonstrated a screen that hosted a silver nanowire circuit as long as 1.2m; enabling it to emit red, green, and blue light with varying biases, as seen in conventional displays. Finally, they showed that when the circuit was deposited onto a polymer substrate, its performance remained stable even when bent to a radius of 15mm – confirming its flexibility.

Thanks to these advantages, Yang’s team believes their technology could eventually replace tin oxide-based circuits in transparent display applications. The next steps in their research will include developing coatings to protect circuits from the surrounding environment; enhancing substrate adhesion; and sandwiching circuits between substrates for better protection and maintenance. With these improvements in place, the technology shows significant promise in allowing for widespread and practical smart displays.

The team report their findings in Optical Materials Express.

Sam Jarman is a science writer based in the UK

This issue explores how researchers in so many areas of materials science are working towards a more sustainable society.

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