These Ballpoint Pens Let You Draw Custom LEDs and Photodetectors, No Bulky Equipment Required

Researchers from Washington University in St. Louis and Florida State University have made a ballpoint pen that allows you to draw custom LEDs or photodetectors on a range of surfaces, by hand.

"Handwriting custom devices was a clear next step after the printer," Chuan Wang, associate professor at Washington University in St. Louis' McKelvey School of Engineering, explains, referring to earlier work the team carried out on developing a means to print flexible LEDs using inkjet printers. "We had the inks already, so it was a natural transition to take the technology we had already developed and modify it to work in regular ballpoint pens where it could be cheap and accessible to all."

The result looks, for all intents and purposes, like any other ballpoint pen: plastic body, ink reservoir, metal nib. Scribble on paper, and it works like one too — but the ink inside is where the magic happens. Filled with what the team describes as as PEDOT:PSS/PEO composite ink, drawings made with the pen can be lit through the application of electricity — creating what they call "PeLEDs" in the shape of your choosing.

"Our method uses common ballpoint pens filled with newly formulated inks of conductive polymers, metal nanowires and multiple perovskites for a wide range of emission colors," the team explains. "Just like writing with multicolored pens, writing layer-by-layer with these functional inks enables perovskite optoelectronic devices to be realized within minutes."

To demonstrate the ink's flexibility, quite literally, the team ran through a range of demonstrations: using the pens to draw LEDs on the inside of a glass vial, on a stretchable sheet of rubber, and on a piece of fabric. In the case of the rubber, the LED continued to operate even when stretched up to 140 per cent across both axes — something traditional conductive inks can struggle to handle.

"To explore the resolution limit of our handwriting fabrication strategy, we attempted to purchase different ballpoint pens available on the market and loaded them with our formulated ink to write on printer paper found in office," the researchers write. "The EL [electroluminescent] images of PeLEDs in various sizes confirm the resolution of handwriting approach could reach sub-200 μm effectively."

The composite ink-loaded pens are usable by anyone, without prior training, the researchers claim, and can also be used to draw custom photodetectors — taking advantage of an LED's ability to work in reverse and detect light rather than emit it.

The team's work has been published in the journal Nature Photonics under closed-access terms.