Mar 18: Researchers from University of Michigan Engineering have uncovered a hidden phenomenon in OLED displays, revealing that what appears to be a uniform glow is actually produced by nanoscale hotspots, some of which flicker—potentially affecting device performance and lifespan. The findings are published in Nature Photonics.
The study shows that light in OLED screens originates from highly localized regions where electrical charge accumulates unevenly. These hotspots can carry significantly higher current than surrounding areas, increasing the likelihood of faster degradation.
“If some areas are carrying more current than others, they’re likely to burn out faster,” said Stephen Forrest, the Peter A. Franken Distinguished University Professor of Engineering and co-senior author of the study. “This phenomenon could affect the reliability and performance of devices—from OLED displays to solar cells and transistors.”
Uneven Charge Flow Creates ‘Hotspots’
The researchers describe the movement of charge carriers—electrons and positively charged “holes”—as flowing through a hilly energy landscape, naturally gravitating toward lower-energy “valleys.” These valleys form high-density charge pathways, or “charge rivers,” where electrons and holes meet to emit light.
However, these pathways can carry 10 to 100 times more charge than other regions, creating nanoscale hotspots. In contrast, crystalline materials provide a more uniform energy landscape, allowing charge to distribute evenly and potentially reducing hotspot formation.
“Charge carriers tend to follow the lowest energy pathways, much like rivers flowing through valleys,” explained Chris Giebink, professor of electrical and computer engineering and co-senior author.
Advanced Imaging Reveals Flickering Phenomenon
Using superresolution optical fluctuation imaging, the team was able to observe hotspots as small as a few tens of nanometers—far below the limits of conventional optical microscopy.
“We confirmed that what we observed was not a microscope artifact, but an electrical phenomenon,” said Joshua Springsteen, Ph.D. student and first author of the study.
The researchers found that some hotspots flicker due to temporary trapping of charge carriers. When carriers get stuck, they block current flow, causing nearby regions to dim. Once released, the hotspot lights up again. These fluctuations occur out of sync, creating the illusion of a steady glow to the human eye.
A Path Toward More Durable Electronics
The study suggests a potential solution: replacing commonly used amorphous (disordered) materials in OLEDs with crystalline structures, which offer a flatter energy landscape and more uniform charge distribution. This could significantly improve device reliability and longevity.
Beyond OLED displays, the findings have broader implications for organic electronics, including solar cells and transistors, where uneven charge flow can impact efficiency and performance.
Innovation and Future Applications
The device used in the study was fabricated at the Lurie Nanofabrication Facility and analyzed at the Michigan Center for Materials Characterization. The research team has filed for patent protection through U-M Innovation Partnerships and is licensed to Universal Display Corporation.
The study was supported by the U.S. Department of Energy and industry partners.
This discovery not only reshapes the understanding of how OLED devices function at the nanoscale but also opens new avenues for designing longer-lasting, more efficient electronic and photonic devices.
