Scientists have been working on various ways to print electronic and optical components using traditional printing techniques to facilitate their fabrication and create more flexible devices.

A team of researchers in Germany now has devised a new way to make organic light-emitting diodes (OLEDs)—which are used in electronic devices ranging from smartphones to televisions—using traditional inkjet printing, opening the future possibility for flexible displays and other novel applications.

OLED, organic light-emitting diodes, Max Planck Institute for Polymer Research, thermally activated delayed fluorescence, TADF, inkjet printing
The first prototype of an organic light-emitting diode developed using inkjet printing by researchers in Germany. (Image Source: Max Planck Institute for Polymer Research)

Scientists led by researchers Gert-Jan Wetzelaer at the Max Planck Institute for Polymer Research (MPI-P) have overcome a key challenge to printing OLEDs by breaking down the different layers typical to fabricating these devices to just one.

Their work paves the way for printing OLEDs that are on-par with current devices in terms of luminosity and efficiency using inkjet technology, he said in a press statement.

OLEDs are different from LEDs in that they use organic compounds based on carbon as a main component rather than the semiconductor material gallium. However, OLEDs lack the same performance and longevity of typical LEDs, which is why scientists are interested in finding ways to optimize both their fabrication and performance.

Breaking It Down

MPI-P researchers decided to chose the former route in their OLED research. Typical OLEDs are comprised of various wafer-thin layers—including some that transport charges and others that introduce electrons into the active layer that generates light, researchers said. In fact, an OLED fabricated today easily can have five to seven layers of material.

Understandably, it’s not so easy to print a multiple-layered device using current printing technology. To tackle this problem, researchers used a light-emitting layer based on what’s called  “thermally activated delayed fluorescence” (TADF), a physical principle known for several decades but only leveraged for about the last 10 years in OLED research.

TADF-based OLEDs don’t require the expensive and complex molecular components that use rare-earth metals currently found in OLEDs, and thus enabled researchers to develop an OLED comprised only of a single layer with two electrodes supplying electricity, Wetzelaer said.

Researchers demonstrated a prototype that generated an emitted-light brightness of 10,000 candela per square meter with a 2.9 volt-device. That brightness level is the equivalent of about 100 times the luminosity of modern screens, researchers reported—a record for currently produced OLEDs, they said.

Researchers also measured continuous operation of the device with a metric called “LT50 lifetime.” The OLED they printed sustained nearly 2000 hours of functionality at a brightness equivalent to 10 times that of modern displays, dropping its initial luminosity to 50 percent of its value during this time, they said.

Researchers published a paper on their work in the journal Nature Photonics.

Researchers plan to improve their design with further research to achieve longer lifetimes for the OLEDs, which would allow them to be used for industrial purposes, Wetzelaer said. They also hope their research will inform other scientists in identifying and improving processes currently responsible for limiting and reducing the luminosity of OLEDs over time, he said.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.

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