Thermally Activated Delayed Fluorescence in Organic Light-Emitting Devices

Thermally activated delayed fluorescence (TADF) has emerged as a transformative mechanism in organic light-emitting devices, enabling near-complete harvesting of triplet excitons in purely organic compounds. By minimising the energy gap between the lowest singlet and triplet excited states, thermal energy at room temperature drives reverse intersystem crossing from the triplet manifold into emissive singlet states. This circumvents the need for heavy-metal phosphors and opens pathways to low-cost, high-efficiency emitters spanning the full visible spectrum. Recent advances in molecular design have focused on optimising donor–acceptor architectures, rigidifying geometries to suppress non-radiative decay, and fine-tuning frontier orbital distributions to achieve both narrow emission bandwidths and high external quantum efficiency. Device architectures now integrate optimised host–guest systems, novel encapsulation strategies and hyperfluorescent configurations to deliver stable deep-blue, green and red devices with lifetimes meeting commercial standards. These developments carry significant implications for next-generation displays, solid-state lighting and energy-efficient signage, offering scalable routes to environmentally benign solutions in lighting technology.

Research from Nature Portfolio

Innovative host–guest systems have been developed in which blue emitters are covalently encapsulated to suppress Dexter energy transfer and obviate the need for high-bandgap matrices. Such matrix-free designs deliver ultranarrowband deep-blue emission with peak external quantum efficiencies exceeding 20%, while transient spectroscopy confirms marked reduction of triplet quenching pathways. In parallel, breakthrough purely organic electroluminescent materials have demonstrated close to 100% photoluminescence quantum yield and near-zero singlet–triplet splitting. Strategic tuning of donor and acceptor moieties yields almost complete triplet-to-singlet upconversion, affording device external quantum efficiencies above 30% even at high luminance. These advances collectively chart a clear trajectory towards commercial-grade, heavy-metal-free OLEDs with unparalleled performance metrics.

Thermally Activated Delayed Fluorescence in Organic Light-Emitting Devices publication trend

The graph below shows the total number of articles in thermally activated delayed fluorescence in organic light-emitting devices across all publications each year (not limited to Nature Index journals).

Technical terms

Thermally activated delayed fluorescence (TADF): Emission process in organic molecules where thermal energy promotes reverse intersystem crossing from triplet to singlet states, enhancing fluorescence yield.

Reverse intersystem crossing (rISC): Upconversion process wherein triplet excitons are converted into emissive singlet states, central to TADF efficiency.

Singlet–triplet energy gap (ΔEST): Energy difference between the lowest singlet and triplet excited states; minimised values enable efficient TADF.

Dexter energy transfer: Short-range, exchange mechanism causing triplet exciton quenching between host and guest molecules.

Multiresonant TADF (MR-TADF): Subclass of TADF emitters featuring rigid, heteroatom-doped frameworks that yield narrowband emission and high colour purity.

External quantum efficiency (EQE): Ratio of emitted photons to injected charge carriers in a device, a key metric of OLED performance.

References

1. Suppression of Dexter transfer by covalent encapsulation for efficient matrix-free narrowband deep blue hyperfluorescent OLEDs. Nature Materials (2024).
2. Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light‐Emitting Diodes. Advanced Materials (2017).
3. Purely organic electroluminescent material realizing 100% conversion from electricity to light. Nature Communications (2015).
4. The Importance of Vibronic Coupling for Efficient Reverse Intersystem Crossing in Thermally Activated Delayed Fluorescence Molecules. ChemPhysChem (2016).
5. The Role of Local Triplet Excited States and D‐A Relative Orientation in Thermally Activated Delayed Fluorescence: Photophysics and Devices. Advanced Science (2016).
6. Multiresonant Thermally Activated Delayed Fluorescence Emitters Based on Heteroatom‐Doped Nanographenes: Recent Advances and Prospects for Organic Light‐Emitting Diodes. Advanced Functional Materials (2020).