Events & News

Events & News

Latest Innovations

Pure-blue single-layer organic light-emitting diodes based on trap-free hyperfluorescence

03 September 2025

Latest Innovations

Recommended Products View More

OLED technology has already matured for high-end displays, blue OLEDs still lag behind their green and red counterparts. Blue fluorescent emitters offer good stability but suffer from limited efficiency because only singlet excitons are harvested. Blue phosphorescent emitters achieve higher efficiency via triplet harvesting, yet their operational stability remains low. Over the past decade, thermally activated delayed fluorescence (TADF) has emerged as a promising alternative, but blue TADF devices likewise exhibit insufficient stability and intrinsically broad spectra that compromise colour purity. To improve colour purity, researchers have proposed introducing a small amount of narrow-band fluorescent emitter into the TADF system and realizing hyperfluorescence through energy transfer. However, this approach risks additional energy losses, and current efforts focus primarily on suppressing Dexter energy transfer—namely, the non-radiative transfer of TADF triplet excitons to the fluorescent emitter. The main countermeasures are (1) employing the fluorescent emitter at an extremely low concentration (1 %–2 %) to reduce short-range Dexter transfer, and (2) adopting TADF emitters with a high reverse intersystem crossing (RISC) rate to decrease the triplet-exciton density.

Recently, Wetzelaer et al. from the Max Planck Institute in Mainz, Germany, published a groundbreaking paper titled "Pure-blue single-layer organic light-emitting diodes based on trap-free hyperfluorescence" in Nature Materials. By ingeniously leveraging the energetic disorder of the TADF sensitizer, they successfully developed a pure-blue hyperfluorescent OLED composed of a single emission layer without the need for charge transport layers, while ensuring that the terminal emitter introduces no charge trapping.

Key Innovation

1. Key Findings: Trap-Free Hyperfluorescence in a Single Layer

The emissive layer is simply a vacuum-deposited ternary blend—mCBP-CN host, DBA-DI TADF sensitizer and 2 wt % ν-DABNA narrow-band terminator—sandwiched between PEDOT:PSS:PFI and Ba/Al electrodes. No electron/hole-blocking layers, no complex grading, no dopant cascades (Figure 1).

Figure 1 Device layout of a pure-blue hyperfluorescent single-layer OLED.

Charge transport becomes more balanced when doping DBA-DI in mCBP-CN. An optimum in terms of charge balance is observed for a DBA-DI concentration in the range of 20%–50% (Figure 2a). Incorporating 2% ν-DABNA has negligible impact on charge transport, indicating no significant trapping occurs despite its smaller bandgap (Figure 2b,c). By fitting temperature-dependent transport data with drift-diffusion simulations under the extended Gaussian disorder model, the DOS widths (σ) are quantified as 0.14 eV for electrons and 0.12 eV for holes. This disorder mitigates trapping by effectively reducing the trap depth, enabling trap-free operation (Figure S4).

Figure 2 Charge transport in the emissive layer.

When the absolute trap depth is less than σ²/2kT, charges are no longer trapped. In this system, σ²/2kT values were 0.28 eV for holes and 0.38 eV for electrons—sufficient to encompass the energy levels of ν-DABNA.

Figure 3 Schematic of the effect of energetic disorder on the trap depth.

Multiscale simulations of the DBA-DI:mCBP-CN blend (40% DBA-DI) confirm hole transport occurs exclusively through DBA-DI, while electron transport is partially assisted by mCBP-CN due to aligned electron affinity distributions. The simulated DOS widths (0.14 eV electrons, 0.12 eV holes) match experimental values. Crucially, ν-DABNA's energy levels fall within DBA-DI's broad transport state distribution, explaining the absence of charge trapping. This mechanistic insight demonstrates general relevance for hyperfluorescent OLED designs leveraging energetic disorder.

Figure 4 Simulated DOS distributions of the emissive layer.

Highly efficient and stable pure-blue hyperfluorescent single-layer OLEDs achieved through trap-free operation. The devices utilize a simplified architecture with PEDOT:PSS:PFI and TPBi/Ba/Al as ohmic contacts, functioning as operational single-layer devices. They exhibit exceptional performance: narrowband emission at 475 nm with 22 nm FWHM, high EQEs of 24-25% with minimal roll-off, and remarkably low operating voltages (2.4-2.5 V). Power efficiencies reach 50-51 lm/W, among the highest reported for narrowband blue hyperfluorescent OLEDs.

Critically, adding ν-DABNA only modifies the emission spectrum without affecting electrical characteristics, confirming exclusive excitation through energy transfer rather than charge trapping. This trap-free operation is attributed to the energetic disorder of the TADF sensitizer. The single-layer architecture provides additional stability benefits by broadening the recombination zone and minimizing exciton-polaron interactions, resulting in an impressive LT₅₀ of 716 hours at 1,000 cd/m², comparable to state-of-the-art devices. These findings demonstrate that single-layer OLEDs can achieve performance rivaling complex multilayer architectures while offering simplified fabrication and enhanced stability.

2. Device Performance: Efficiency, Color Purity, and Stability

The resulting single-layer hyperfluorescent OLEDs exhibited exceptional performance:

• High EQE and Power Efficiency: External quantum efficiency reached 25%, with power efficiency up to 51 lm/W—among the highest reported for narrow-band blue hyperfluorescent OLEDs (Figure 5a).

• Pure-Blue Emission: Electroluminescence peaked at 475 nm with a narrow full-width at half-maximum (FWHM) of 22 nm, enabling high color purity (Figure 5c).

• Low Operating Voltage: Turn-on voltages as low as 2.4 V were achieved, well below the optical bandgap of ν-DABNA, thanks to balanced charge transport and the absence of heterojunctions.

• Excellent Operational Stability: The devices showed an LT₅₀ lifetime of 716 hours at an initial luminance of 1,000 cd/m²—comparable to the best reported hyperfluorescent blue OLEDs (Figure 5d).

Figure 5 Device performance of single-layer pure-blue hyperfluorescent OLEDs.

Conclusion

This work provides a new design rule for hyperfluorescent systems: energetic disorder should be considered a key parameter that can enable the use of smaller-gap emitters without compromising performance. These findings pave the way for more efficient, stable, and pure-blue OLEDs—bringing us closer to the goal of full-color, high-performance displays and lighting systems that are both energy-efficient and durable.

AmBeed's Products Support Related Research

In the above study, mCBP-CN acts as the electron-transporting host, DBA-DI functions as the sensitizer for charge transport and energy transfer, and v-DABNA serves as the narrowband terminal emitter for pure-blue hyperfluorescence. At AmBeed, we provide these products along with more TADF materials to support your research in developing high-performance hyperfluorescence OLED devices.

mCBP-CN，A2872218

DBA-DI，A2954281

v-DABNA，A1324629

Explore our TADF materials to improve your OLED efficiencies (>200 compounds)

Thermally activated delayed fluorescence (TADF) materials are a class of organic emitters that enable highly efficient light emission through a unique mechanism called reverse intersystem crossing (RISC). Unlike conventional fluorescent materials, TADF harnesses both singlet and triplet excitons by thermally repopulating singlet states from triplets, achieving nearly 100% internal quantum efficiency. This eliminates the need for rare-metal dopants (e.g., iridium or platinum) used in phosphorescent systems, reducing costs and environmental impact. TADF materials are pivotal in organic light-emitting diodes (OLEDs) for displays and lighting due to their high efficiency, tunable emission colors, and potential for long operational lifetimes.

TADF materials

References

[1]Sachnik O, Kinaret N, Saxena R, et al. Pure-blue single-layer organic light-emitting diodes based on trap-free hyperfluorescence[J]. Nature Materials, 2025.

Prev: Chemoselective synthesis of 1,3,4-thiadiazoles from acyl hydrazines and nitroalkanes using elemental sulfur

Next: Decoding Prostate Cancer: The Molecular Blueprint and Targeted Treatment Landscape (Part I)