Ann Arbor Times

Screens for televisions, smartphones, and other displays may soon incorporate a new organic LED material developed by an international team led by engineers from the University of Michigan. This innovative material aims to maintain sharp color and contrast while eliminating the need for heavy metals.

Currently, OLED devices use heavy metals like iridium and platinum to enhance efficiency, brightness, and color range. However, these metals increase costs, reduce device lifespan, and pose health and environmental risks.

The challenge with OLEDs is that phosphorescence, preferred over fluorescence for its energy efficiency, occurs slowly without heavy metals. To avoid "ghost" images on screens operating at 120 frames per second, phosphorescence must happen in microseconds—a task traditionally managed by heavy metals.

"We found a way to make a phosphorescent organic molecule that can emit light on the microsecond scale, without including heavy metals in the molecular framework," stated Jinsang Kim from the University of Michigan. He co-authored the study published in Nature Communications alongside Dong Hyuk Park from Inha University and Sunkook Kim from Sungkyunkwan University.

The research details how electrons behave within OLED materials during light emission. In fluorescence, electrons release energy immediately as light; however, phosphorescence requires an electron spin conversion before emitting light. Heavy metal nuclei have been used to facilitate this process through magnetic fields.

The new material employs a two-dimensional layer of molybdenum and sulfur near an organic layer to achieve similar effects through physical proximity rather than chemical bonding. This design increases light emission speed by 1,000 times—adequate for modern displays—while potentially extending material longevity.

This hybrid system also challenges existing quantum mechanical understanding by suggesting paired electrons share an orbital with combined spins under dark conditions—a scenario previously deemed impossible due to the Pauli Exclusion Principle.

"We don’t yet fully understand what causes this triplet character in the ground state because this violates the Pauli Exclusion Principle," Kim noted. "That is very impossible, but looking at the measurement data, yes, that seems to be the case."

Further exploration into these phenomena will continue as researchers also seek applications in spintronics devices. The team has applied for patent protection with U-M Innovation Partnerships' assistance and is looking for partners to develop devices using this new material type.

This research received support from Korea's National Research Foundation grant funded by the Korean government and a START grant from U-M College of Engineering. Collaborators included experts from UC Berkeley and Dongguk University.