Synopsis

How Quantum Effects Shape OLED Performance

Physics 18, s74
Two studies elucidate key mechanisms limiting the efficiency and stability of organic light-emitting diodes.
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Compared with their rivals, displays based on organic light-emitting diodes (OLEDs) can offer sharper images, higher refresh rates, and wider viewing angles. However, they can also have a shorter lifespan and a lower peak brightness because of the limited stability and efficiency of OLEDs. Now two reports have shed light on previously uncertain processes responsible for these shortcomings [1, 2]. This improved understanding could help scientists create better-performing OLEDs.

In an OLED, electrons and holes—electron vacancies—pair up to form excited states known as excitons. If an exciton has a total spin of 0, it is called a singlet and quickly transitions to its ground state, emitting a photon. But if it has a spin of 1, it is called a triplet and typically loses its energy as heat before it can transition. Each team focused on a type of OLED in which a different mechanism converts this otherwise wasted energy into light. Both types suffer from low efficiency at high brightness and from degradation because of detrimental interactions of triplets with singlets, with other triplets, and with quasiparticles called polarons.

Gert-Jan Wetzelaer at the Max Planck Institute for Polymer Research in Germany considered OLEDs that use a process known as thermally activated delayed fluorescence [1]. Here, after a delay, ambient temperature fluctuations transform triplets into photon-emitting singlets. In his theoretical work, Wetzelaer derived a new expression for the triplet lifetime in these OLEDs. He found that this lifetime governs the stability and high-brightness efficiency of these OLEDs and is well approximated by a quantity that can be easily measured in the lab. These findings thus suggest a simple way to predict how well such OLEDs will perform.

Meanwhile, Clint van Hoesel and his colleagues at Eindhoven University of Technology in the Netherlands analyzed OLEDs that contain heavy-metal atoms [2]. These atoms induce a strong spin–orbit coupling, which allows triplets to directly emit photons, albeit more slowly than singlets do. In their theoretical study, the researchers found that the adverse triplet–polaron interactions in these OLEDs are more complex than previously thought. Instead of involving only dipole–dipole couplings, these interactions also feature, and are sometimes dominated by, overlooked dipole–quadrupole couplings. This insight resolves a long-standing discrepancy between theory and experiment and could lead to more accurate models of these OLEDs.

–Ryan Wilkinson

Ryan Wilkinson is a Corresponding Editor for Physics Magazine based in Durham, UK.

References

  1. G. A. H. Wetzelaer, “Lifetime of triplet excitons in organic LEDs based on thermally activated delayed fluorescence,” Phys. Rev. B 111, L241201 (2025).
  2. C. van Hoesel et al., “Dipole-quadrupole coupling in triplet exciton-polaron quenching in a phosphorescent OLED emission layer,” Phys. Rev. B 111, 224204 (2025).

Subject Areas

OptoelectronicsMaterials Science

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