This Common Ballpoint Pen Can Draw, Write Custom LEDs — How?

Researchers at the McKelvey School of Engineering at Washington University in St. Louis have developed ink pens that allow anyone to handwrite flexible, stretchable optoelectronic devices on everyday materials.

These devices, such as light-emitting diodes (LEDs) and photodetectors, can be handcrafted on surfaces like paper, textiles, rubber, plastics, and even 3D objects.

This innovative approach to fabrication aims to simplify the process of creating custom LEDs and photodetectors, making it accessible to individuals without specialized training or equipment.

Uncomplicated Fabrication Method

The team's breakthrough outlines an uncomplicated and versatile fabrication method that enables individuals to craft custom light-emitting diodes (LEDs) or photodetectors without requiring specialized training or bulky equipment.

This technology is a continuation of earlier work by Wang and Junyi Zhao, a doctoral candidate in Wang's lab. It showcases a novel approach using a simple inkjet printer to fabricate stretchable LEDs.

"Handwriting custom devices was a clear next step after the printer," Wang stated. "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 user-friendly handwriting technique allows for the creation of multicolor LEDs and photodetectors within minutes. The mechanism employs a standard ballpoint pen loaded with specially formulated inks comprised of conductive polymers, metal nanowires, and perovskites.

The team reported that applying these functional inks layer by layer, similar to using multicolored pens, facilitates the cost-effective, swift production of various functional devices, including disposable electronics like smart packaging and personalized wearables like biomedical sensors.

From Printer Ink to Standard Ballpoint Pens

However, the transition from printer ink to standard ballpoint pens was more intricate than it seemed, requiring adjustments to ensure compatibility with porous and fibrous substrates like paper and textiles.

Apart from the visual concern of smudging, the ink layers must remain distinct to maintain high-performance optoelectronic devices.

"Our ink is specially formulated, so the pens are universal, meaning they'll work on almost all substrates. Each single layer of the device is designed to be intrinsically elastic so it will survive deformation and can be bent, stretched and twisted without impacting device performance," Zhao explained.

"For example, LEDs drawn on a glove could tolerate deformations from repeated fist grasping and releasing, and LEDs drawn on a rubber balloon could survive inflation-deflation cycles over and over," he added.

This development overcomes the limitations of traditional LED fabrication, which requires flat, smooth substrates and expensive clean-room fabrication equipment.

The team claimed that it paves the way for wearable electronics to become a common part of daily life in various applications, from education to medical sensors, and beyond. The findings of the research team were published in the journal Nature Photonics.