Researchers at the Pritzker School of Molecular Engineering at the University of Chicago have developed a stretchable OLED display. The new material can bend in half or stretch to more than twice its original length while still emitting a fluorescent pattern.
‘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,’ said Sihong Wang, an assistant professor of molecular engineering at UChicago.
‘This is the class of material you need to finally be able to develop truly flexible screens,’ added Juan de Pablo, the UChicago 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.’
The displays on most high-end smartphones, as well as a growing number of televisions, use OLED (organic light-emitting diode) technology, in which small organic molecules are sandwiched between conductors. When an electrical current is switched on, the molecules emit a bright light. The technology is more energy efficient than older LED and LCD displays, and produces sharp pictures. However, the molecular building blocks of OLEDs have tight chemical bonds and stiff structures.
‘The materials currently used in these state-of-the-art 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.’
Wang and de Pablo knew what it takes to imbue stretchability into materials – long polymers with bendable molecular chains –and also knew which molecular structures were required for an organic material to emit light very efficiently. They set out to create new polymers that integrated both properties.
‘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 optimised.’
Armed with computational predictions for new flexible electroluminescent polymers, they built several prototypes. Just as the model had predicted, 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.
According to Wang, bendable materials that emit light 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.
‘My overall dream is to make all of the essential components for a full system of wearable electronics, from sensing to processing to displaying information,’ Wang explained. ‘Having this stretchable light-emitting material is another step toward that dream.’
The team is now planning to develop new iterations of the display that integrate additional colours into the fluorescence and improve the efficiency and performance. ‘The goal is to eventually get to the same level of performance that existing commercial technologies have,’ said Wang.
The research has been published in Nature Materials.