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With more and more reliance on screens comes a need to make organic light-emitting diodes (OLEDs) more efficient and long lasting. Yi-Zhong She et al review the current landscape of thermally activated delayed fluorescence emitters (TADF) and the potential road ahead in increasing their efficiency in Chemical Science.

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Organic light-emitting diodes (OLEDs) are increasingly common in high end phones and TVs thanks to their energy efficiency, lower voltage requirements and faster responses to voltage changes. As a new technology, there’s still a lot to be done to make them suitable for all screens – OLEDs are still expensive to produce and more susceptible to burn-in on screens.

With a need for more powerful, aesthetically appealing screens in today’s world, scientists have been working on ways to mitigate the drawbacks of OLEDs. Traditional fluorescent materials can only utilise singlet excitons, meaning 75% of energy is wasted.

In their review article, Yi-Zhong She et al explore the use of phosphorescence and thermally activated delayed fluorescence (TADF) emitters to minimise energy waste and create brighter results. 

Enabling greener, more energy efficient emitters

Despite their heavy use in commercial technologies, there are many drawbacks to phosphorescence-based OLEDs. They’re expensive, and have high levels of toxicity due to heavy atoms and a lack of stable blue emitters. Using TADF-based OLEDs instead is a suitable alternative with a potential of 100% efficiency and energy use.

Throughout this insightful article from Yi-Zhong She et al, the advantages and disadvantages of various acceptors are explored, including cyano-substituted, carbonyl-substituted or sulfone-substituted aromatic organic compounds, nitrogen-containing heterocycles, and finally, boron-based units.

They argue that there are two main TADF-based OLED molecular design strategies:

• Positioning adjacent luminescent materials further away from each other
• Adding spacers within the molecules to distance the reactive cores

Future advances in OLED efficiency

Thanks to these molecular design strategies, OLED devices that are more efficient and have increased longevity have been developed in the past decade. However, there are still some challenges in creating these new OLED devices, with red OLED devices lacking the efficiency of blue and green OLEDs.

Further issues are also present, with some TADF-based non-doped OLEDs displaying short lifespans compared to their doped counterparts.

TADFs have shown incredible progress and development through the years. It remains imperative that research on using novel TADF emitters for non-doped OLEDs continues to create more efficient OLEDs with minimal drawbacks.

This article is free to read in our open access, flagship journal Chemical Science: Ting Lei et al, Chem. Sci., 2023.