A bended piece of what looks like glass glows green, showing LED properties

Inkjet-printed LEDs pave way for bendable digital displays

As anyone who has panicked after dropping a smartphone would know, most electronics screens are unforgiving, solid rectangles. But Washington University in St. Louis researchers developed a new material that could allow digital displays to be so flexible they can roll up and fit into a pocket. 

The technology

Researchers working under Chuan Wang, an assistant professor of engineering, have developed a material that combines two common display technologies: light-emitting diodes, or LEDs, and organic LEDs, or OLEDs. Organic LEDs are cheap and flexible “but they have relatively low performance and short lifetime,” Wang said in a news release. “Inorganic LEDs such as microLEDs are high performing, super bright and very reliable, but not flexible and very expensive.”

The WUSTL team’s innovation is an organic-inorganic crystalline material called an organometal halide perovskite. Perovskites are often used to make items like LED screens or solar panels. In the usual LED-making process, liquid perovskites are dripped onto a spinning surface and eventually spread out.  

That spinning process results in a stiff LED and also wastes perovskites as the liquid flies off the work surface. The WUSTL researchers instead fabricated their perovskite with an inkjet printer that was less wasteful and much faster — the process takes about 25 minutes compared with five hours.

Another benefit of the inkjet process is that it would allow perovskites to be printed onto nontraditional, flexible substances. But perovskites themselves are rigid, and couldn’t simply bend if they were printed on a substance like rubber. So to make the perovskites more flexible, Junyi Zhao, a PhD candidate in Wang’s lab, embedded the inorganic perovskites into an organic polymer. That allowed the perovskite, and the LEDs it makes up, to become bendable and stretchy. 

What’s next

WUSTL has a patent pending for this technology and fabrication method. LEDs created in this way could be used for wearable devices, like watches that can stretch around the wearer’s wrist, or in digital screens that can be embedded into walls. And beyond that, unlocking the ability to print stretchy electronics faster and more cheaply allows for the creation of new technologies that haven’t been thought of yet.

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