The material is said to have a wide range of applications, from wearable electronics and health sensors to foldable computer screens.
“One of the most important components of nearly every consumer electronic we use today is a display, and we’ve combined knowledge from many different fields to create an entirely new display technology,” explained Sihong Wang, assistant professor of molecular engineering, who led the research with Juan de Pablo, Liew Family Professor of Molecular Engineering.
“This work is really foundational, and I expect it to allow many technologies that we haven’t even thought of yet,” added de Pablo.
Displays on many devices use OLED (organic light-emitting diode) technology, which sandwiches small organic molecules between conductors, and when an electrical current is switched on, the small molecules emit a bright light. The technology is more energy-efficient than older LED and LCD displays and provides much sharper pictures. However, the molecular building blocks of OLEDs have tight chemical bonds and stiff structures.
“The materials currently used in OLED displays are very brittle; they don’t have any stretchability,” said Wang. “Our goal was to create something that maintained the electroluminescence of OLED but with stretchable polymers.”
To imbue stretchability into materials, long polymers with bendable molecular chains are required, and the molecular structures were also required to emit light very efficiently.
“We have been able to develop atomic models of the new polymers of interest and, with these models, we simulated what happens to these molecules when you pull on them and try to bend them,” explained de Pablo. “Now that we understand these properties at a molecular level, we have a framework to engineer new materials where flexibility and luminescence are optimized.”
Using computational predictions for new flexible electroluminescent polymers, the team was able to build several prototypes in which the materials were flexible, stretchable, bright, durable and energy efficient.
A key feature in their design was the use of “thermally activated delayed fluorescence,” which let the materials convert electrical energy into light, in a highly efficient way. This third-generation mechanism for organic emitters can provide materials with performance on par with commercial OLED technologies.
Wang has previously developed stretchable neuromorphic computing chips that can collect and analyse health data on a kind of flexible Band-Aid. The ability to now create stretchable displays adds to his growing suite of tools for next-generation wearable electronics.
Bendable materials that emit light, he said, can not only be used to display information, but can be integrated into wearable sensors that require light. Sensors measuring blood oxygenation and heart rate, for instance, typically shine a light through blood vessels to sense blood flow.
Wang said a bendable light-up material also could, eventually, be integrated into implantable devices, such as those that use light to control the activity of neurons in the brain (this kind of so-called optogenetics is currently used only in animal experiments to better understand the brain and brain diseases).
The team is planning to develop new iterations of the display in the future, integrating additional colours into the fluorescence and improving the efficiency and performance.
