New discovery substantially increases the brightness of OLED displays

Organic light-emitting diodes (OLEDs) are transforming modern lighting and display technology with their slim profile, lightweight structure, and flexible designs. Unlike traditional light sources, OLEDs emit their own light without requiring a backlight, making them ideal for high-definition screens in smartphones, laptops, and TVs.

However, a fundamental limitation restricts their brightness. Due to spin statistics, only 25% of the electrical excitations produce light efficiently, while the remaining 75% exist in dark triplet states that typically fail to contribute to illumination.

This inefficiency affects OLED brightness, making them dimmer than traditional LEDs. Scientists are now looking at quantum physics to solve this issue, particularly by harnessing special hybrid light-matter states known as polaritons.

Polaritons form when organic molecules interact with confined light between two semi-transparent mirrors. This coupling creates new quantum states that can influence energy transfer inside OLEDs. By fine-tuning these states, researchers have discovered that dark triplet states can be converted into bright polaritons, significantly improving light output.

A study led by researchers from the University of Turku, Finland, and Cornell University, USA, developed a theoretical model predicting substantial brightness increases in OLEDs by leveraging polaritons. The team explored how the number of coupled molecules influences this effect.

“While the general idea of using polaritons in OLED technology is not entirely original, a theory that examines the boundaries of performance gains has been missing. In this work, we carefully examined where the polariton sweet spot lies in different scenarios,” said Associate Professor Konstantinos Daskalakis from the University of Turku.

Their findings revealed that strong coupling works best when only a single molecule is involved. With this setup, the dark-to-bright conversion rate increased by an astonishing factor of 10 million.

However, when too many molecules were coupled, the polaritonic effect diminished significantly. This means that merely adding mirrors to OLEDs will not enhance efficiency unless single-molecule strong coupling is achieved.

In addition to polaritons, another method to improve OLED efficiency involves thermally activated delayed fluorescence (TADF). Emitters displaying TADF can convert dark triplet excitations into bright singlets using a process called reverse inter-system crossing (RISC).

However, designing molecules with high RISC rates is challenging, as it often weakens fluorescence strength. Scientists have been searching for alternative ways to achieve high RISC rates without reducing light output.

Polaritons may provide a solution. Because they act as artificially Stokes-shifted singlet states, they can enable high RISC rates while maintaining strong fluorescence. This breakthrough could allow OLEDs to achieve both high internal quantum efficiency (IQE) and superior brightness.

While some experimental results confirm this approach, theoretical models remain underdeveloped. More research is needed to fully understand how polaritons interact with molecular energy processes inside OLEDs.

Despite the promising potential of polariton OLEDs, integrating this technology into commercial products presents challenges. The first hurdle is finding ways to achieve strong coupling at the single-molecule level.

Standard OLED designs involve a high number of molecules, which dilutes the polaritonic effect. Researchers must either develop architectures that facilitate single-molecule coupling or engineer new materials tailored for polaritonic applications.

“The next challenge is to develop feasible architectures facilitating single-molecule strong coupling or invent new molecules tailored for polariton OLEDs. Both approaches are challenging, but as a result, the efficiency and brightness of OLED displays could be significantly improved,” Daskalakis explained.

Another issue is material selection. The effectiveness of polaritonic OLEDs depends on the specific organic molecules used. These materials must not only support strong light-matter interactions but also retain their stability and efficiency over time. Discovering new organic compounds capable of maintaining high performance under real-world conditions is crucial to making this technology viable.

The widespread adoption of OLEDs has been hindered by efficiency and brightness limitations compared to inorganic LEDs. However, advances in polariton physics and TADF research could soon change this landscape. By finding ways to harvest triplet states effectively, OLEDs may achieve unprecedented levels of brightness and efficiency.

This research lays the foundation for OLEDs that are not only more efficient but also capable of achieving performance levels once thought impossible.

If successfully implemented, these developments could lead to brighter, longer-lasting, and more energy-efficient displays, revolutionizing the future of screen technology.

Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.

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