Hyperfluorescence represents a significant advancement in light-emitting technology in organic light-emitting diodes (OLEDs). It combines conventional fluorescence with thermally activated delayed fluorescence (TADF). This innovative approach allows for enhanced brightness and improved performance in display and lighting applications. Introduced around 2014, hyperfluorescence is considered the fourth generation of OLED technology, building upon earlier fluorescent, phosphorescent, and TADF-only systems. It offers a pathway to achieve high external quantum efficiencies and precise color emission, setting a new standard for light production.
Understanding Fluorescence and Hyperfluorescence
Fluorescence is a phenomenon where a substance absorbs light at one wavelength and then re-emits it at a longer wavelength. In an OLED, when electrical current passes through the emissive layer, it creates excited states known as excitons. In traditional fluorescent OLEDs, only a quarter of these excitons, singlet excitons, can efficiently produce light. The remaining three-quarters are triplet excitons, which are typically lost as heat, limiting the overall efficiency to about 25%.
Hyperfluorescence overcomes this limitation by incorporating thermally activated delayed fluorescence (TADF) materials. These TADF materials act as “sensitizers” that convert the unused triplet excitons into useful singlet excitons via reverse intersystem crossing (RISC). This conversion is thermally assisted, meaning it uses thermal energy within the device to “up-convert” the triplet states to singlet states.
Once converted, singlet excitons from the TADF sensitizer transfer their energy to a distinct fluorescent emitter molecule. This energy transfer occurs via Förster Resonance Energy Transfer (FRET), a non-radiative process where energy moves from the excited singlet state of the sensitizer to the singlet state of the fluorescent emitter. The fluorescent emitter then emits light. This multi-component system, involving a host material, a TADF sensitizer, and a fluorescent emitter, enables nearly 100% of all generated excitons—both singlet and triplet—to contribute to light emission.
Key Advantages of Hyperfluorescence
Hyperfluorescence offers several benefits over previous light-emitting technologies, primarily by harvesting all excitons for light production. This complete exciton utilization leads to very high energy efficiency, as very little energy is lost as heat. Unlike earlier phosphorescent or TADF-only emitters, hyperfluorescence achieves this high efficiency while also producing a narrow emission spectrum.
A narrow emission spectrum provides improved color purity and a wider color gamut for displays. This means that devices using hyperfluorescence can reproduce colors more accurately and vibrantly without needing filters to remove unwanted wavelengths, which would otherwise reduce brightness and efficiency. The narrow spectrum also allows for higher peak brightness at lower current levels. Driving OLEDs with lower currents not only conserves power but also contributes to a longer operational lifespan for the organic materials.
Hyperfluorescence also avoids rare and expensive metals like iridium, which are often used in phosphorescent emitters. This makes hyperfluorescence a more cost-effective and sustainable solution for large-scale manufacturing. The combination of high efficiency, high color purity, and extended device longevity positions hyperfluorescence as an attractive alternative for advanced display and lighting applications.
Current and Future Applications
Hyperfluorescence technology impacts organic light-emitting diodes (OLEDs), especially in displays. It is being integrated into high-definition televisions, advanced mobile devices, and immersive virtual reality systems. The technology allows for wider color gamut displays due to its narrowband emission and high external quantum efficiencies.
In display applications, the enhanced color purity and higher peak brightness offered by hyperfluorescence translate into more vivid and true-to-life images. This efficiency also means that displays can consume less power, especially in high dynamic range (HDR) content, where bright areas require more light output.
Beyond displays, hyperfluorescence holds promise for various general lighting applications needing energy efficiency and color quality. The technology’s ability to achieve high performance without relying on expensive rare metals makes it an attractive option for broader commercial adoption. Ongoing research continues to refine hyperfluorescence materials and device structures, with efforts focused on optimizing host materials and mitigating energy loss mechanisms to further enhance performance, especially for blue emitters.