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Perovskite LEDs produced by penmanship

15 Aug 2023

WUSTL technique deposits flexible optoelectronic devices on everyday materials.

The potential advantages of perovskite materials for both light emission and absorption in optoelectronic devices have been clear for some time.

In photovoltaic devices, perovskites hold out the promise of greener alternatives to silicon solar cells, although manufacturing such materials at scale has remained challenging.

For light emission, perovskite-based LEDs may prove to be a route to low-cost, color-tunable approaches to device design for color displays and lighting, and for uses in optical communication applications.

A project at Washington University in St. Louis (WUSTL) has now developed a method of depositing perovskite optoelectronic structures from handheld ink pens, leading to emitters being "written" by hand on flexible, stretchable materials.

Published in Nature Photonics, the findings could allow anyone to make a custom LED or photodetector without the need for any specialized training or bulky equipment.

The new handheld fabrication technology builds on earlier work by WUSTL studying how to create stretchable LEDs using a simple inkjet printer, depositing the optoelectronic materials required through the same principles that the printer uses to deposit pigment.

"Handwriting custom devices was a clear next step after the printer," said WUSTL's Chuan Wang. "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 project aimed to design handheld writing instruments filled with inks made of conductive polymers, metal nanowires and perovskite materials to generate a wide spectrum of emission colors. By building up layers of the functional inks with the pens, a variety of functional devices including disposable electronics, smart packaging, and personalized biological sensors could be created cheaply, easily and quickly.

Clinical benefits for medical patients from handwritten devices

"Strategies for fabricating light-emitting diodes and photodetectors on different substrates are restricted in terms of their quantity and variety as strict flatness and smoothness are often required," noted the project in its Nature Photonics paper. "Here we develop a highly versatile, scalable and eco-friendly handwriting approach to draw multicolour perovskite light-emitting diodes and perovskite photodetectors on various substrates."

The translation of the principle from inkjet printer to handheld pen was not trivial, but once achieved means that devices built up from the ink materials could in theory be deposited on almost any substrate.

"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," commented researcher Junyi Zhao. "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."

Creation of LEDs on substrates as varied as fabric and party balloons would potentially overcome limitations of traditional LED fabrication, particularly the requirement of flat, smooth substrates and costly clean-room fabrication equipment. It could ultimately assist next-generation wearable electronics to become widespread in daily life.

Chuan Wang envisions future applications for handwritten electronics ranging from educational purposes and science popularization to electronic packaging, from clothing to medical sensors and bandages.

"One area we’re really excited about is medical applications," Wang said. "Handwritten light emitters and detectors allow more patient-specific flexibility in creating wearable biomedical sensors and bandages that could have photodetectors and infrared LEDs drawn onto them, for measuring pulse oximetry or to speed wound healing."

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