Even in our digital age, pens are an indispensable tool for recording flashes of inspiration or when signing legally binding documents. The ink flowing through them has always been a passive absorber of light, but Juni Zhao of Washington University in St. Louis and colleagues have changed that trend. The team has designed a chemical that writes with ink that produces light similar to a light-emitting diode (LED).
The pen is mightier than the sword, especially with newly designed inks that let writers express themselves in bright, hand-scribbled LEDs. Read more in this story by @SarahESWells. https://t.co/iMBsKswDYY
— Physics Magazine (@PhysicsMagazine) September 14, 2023
LEDs are used in everything from television screens to light bulbs. These are often made using highly tunable semiconductor materials called halide perovskites. However, these devices have traditionally been time- and energy-consuming to manufacture, and they do not easily adhere to non-uniform substrates such as cloth and plastic.
To address these issues, Zhao and his colleagues have turned to a slightly different manufacturing process that is both fast and user-friendly—that of ballpoint pens. The idea stemmed from earlier work by the same team, in which they used an inkjet printer to create perovskite LEDs on non-solid surfaces. “Inkjet printers are common, but the pen is a more widespread tool that can be easily used by both scientists and the general public,” Zhao said. Beyond its innovation, the team also believes that this pen could have applications in the design of flexible electronic textiles (e-textiles), smart packaging and portable electronics that are highly adaptable and fast to manufacture.
https://t.co/DnIukfOPfv👕🤖 Heard of e-textiles? Electronic components are integrated into them to create wearable devices such as smart clothing that monitors vital signs and interactive fashion. @IDTechEx ‘s research shows e-textiles may have a greater role. By @jasmeenGdugal pic.twitter.com/uv3AG6Q6kK
— fashionabc (@fashionabc_) March 31, 2023
To make this possible, Zhao and his colleagues created four different “inks” that must be layered on top of each other using a set of pens. The first ink to be applied is a conductive polymer that penetrates the fabric or other substrate to help create a smooth surface for subsequent layers. The next ink is a perovskite material that is diluted with a solvent. The third ink is another polymer that forms a buffer layer, and the last is a conductive ink that contains silver nanowires.
The researchers calibrated the ink’s viscosity and other properties to resemble those of traditional pen inks. “This deliberate alignment with the properties of the ink makes writing easier, thus mimicking what we do in everyday life,” Zhao said.
The team’s researchers applied these inks to everyday substrates—such as a glass bottle, a rubber balloon, and a synthetic glove. The layers of ink are connected to a small battery and thus emissions can be observed in different colors – red, green and blue, depending on the perovskite used. The team measured the luminance (light intensity per unit area) of the LEDs and found maximum values of about 15,000 candelas per m2, which is several times higher than a mobile phone screen.
Zhao and his colleagues were able to produce these ink-based LEDs in minutes and found that ballpoint pens could apply the layers to uneven surfaces better than inkjet printing and more evenly than roller printing. They also found that the LEDs withstand multiple bends, twists, folds and bulges, depending on the different surfaces.
Sam Strunks, a physicist at the University of Cambridge, and Wei Liu, a materials scientist at the University of Chicago, agree that the discovery will open new doors in the study of flexible electronics that interact with light, such as photodetectors and solar cells. However, they also believe that future work in this direction will need to investigate the consistency and durability of this method of application.
“It’s still a challenge to pen each layer without damaging the layers below,” Liu said. “Further research could delve into optimizing the printing process to ensure consistent performance and long-term reliability.”
Stranks added that the team will need to test whether the pens can operate without loss of performance for extended periods of time. “The demonstrations in the paper are somewhat promising, but more testing will be needed to demonstrate the possibility of sustained operation,” he said.
Besides promoting new areas of research, Zhao said the pen could become part of popular science demonstrations. “We are looking to collaborate with educational toy companies in developing a product based on this technology that could introduce applied and fundamental physics concepts into elementary school classrooms,” he said.