Some phone makers already offer foldable phones, but what if you could roll up the screen and carry it in your wallet? Or wear it on your wrist like a watch? The next step in developing digital displays at Washington University's McKelvey School of Engineering in St. Louis could make this a reality. Researchers in the lab of Chuan Wang, an associate professor in the Preston M. Green Department of Systems engineering and Electrical Engineering, have developed a new material that has the advantages of both LED and OLED technologies and a new manufacturing method -- using an inkjet printer.
The researchers were able to solve this problem by embedding inorganic perovskite crystals into organic polymer matrices made of polymer binders. This makes the peroxide and PeLED themselves elastic and stretchable. The process is not entirely simple. The biggest hurdle, the researchers agree, is making sure the different layers of materials don't mix.
Because all parts of PeLED are made of liquid -- layers of perovskite as well as two electrodes and a buffer layer -- a major problem is keeping all layers unmixed.
Leds are constructed like a sandwich, with at least one emitting layer, one anode layer and one cathode layer. It is sometimes possible to use other layers. The researchers had to keep the perovskite layer from mixing with any other layer, like a highlighter on freshly written ink. They needed to find a suitable polymer, one that could be inserted between the peroxide and other layers, protecting it without interfering too much with PeLED's performance.
"We found the best material and the best thickness to balance the performance and protection of the device," the researchers said. He then went on to print the first elastic PeLEDs.
The university's Office of Technology Management is applying for patents on the technology and manufacturing method. These PeLEDs may be just the first step in an electronic revolution. They can be used to make wearables, or even smart wearables, such as pulse oximeters, which measure blood oxygen. Most exciting, the researchers believe, is that being able to print elastic PeLED cheaply and quickly could lead to new technologies that have yet to be dreamed of.