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What is TADF OLED?

What is TADF OLED?

Thermally Activated Delayed Fluorescence (TADF) OLEDs are the third generation of OLED technology, which maximizes internal quantum efficiency (IQE) by utilizing the transition between triplet excitons and singlet excitons. This is achieved through a unique mechanism called reverse intersystem crossing (RISC), which enables triplet excitons to be converted into singlet excitons and subsequently emit light as delayed fluorescence. This advancement allows TADF OLEDs to achieve nearly 100% IQE, surpassing the limitations of traditional fluorescent and phosphorescent OLEDs.

TADF OLED vs. OLED

Traditional OLEDs rely on two primary mechanisms for light emission：

  • Fluorescent OLEDs represent the first generation of OLED technology. They emit light through singlet excitons. Due to the electronic energy level characteristics of materials, triplet excitons cannot transfer to singlet excitons, resulting in triplet excitons being lost as heat. Therefore, the theoretical efficiency limit of fluorescent OLEDs is 25%, which restricts the development of device efficiency.

  • Phosphorescent OLEDs represent the second generation of OLED technology. They typically use materials containing noble metals such as iridium or platinum. Through orbital coupling between the noble metal and organic ligands, triplet excitons can transfer to singlet excitons, enabling 100% theoretical efficiency. However, phosphorescent emitters are expensive due to the use of noble metals. Additionally, blue phosphorescent OLEDs still face issues of limited lifespan, while high-efficiency red and green phosphorescent OLEDs have been commercially produced for years.

 In comparison, the third-generation TADF OLEDs rely entirely on organic materials to achieve 100% IQE without relying on costly noble metals. By designing twisted structures between electron-donating and electron-accepting groups, the energy gap (ΔEST) between singlet (S₁) and triplet (T₁) states is minimized. This enables the RISC mechanism to operate effectively, making TADF materials a promising solution in OLED technology with high efficiency and low cost.

Common TADF OLED material structures include carbazole, cyano, and triazine groups, such as 4CzIPN, 4CzPN, t4CzIPN, and Cz-TRZ2. These materials are known for their high charge transfer efficiency and tunable emission spectra, making them particularly suitable for improving device efficiency and stability.

 What is MR-TADF OLED?

Multi-Resonance Thermally Activated Delayed Fluorescence (MR-TADF) OLEDs represent an advanced development of TADF materials. Their key feature is narrowband emission (full-width at half maximum, FWHM < 40 nm), achieved through conjugated planar molecular designs that suppress molecular vibration transitions and localize electron density distributions. These characteristics give MR-TADF materials significant advantages in achieving high color purity and high efficiency.

Common MR-TADF materials include boron-nitrogen heterocyclic emitters such as DABNA-1, CzBN, ν-DABNA, and 2PTZBN. These materials exhibit high color purity and device efficiency, making them particularly suitable for display applications.

TADF OLED Advantage and Application

Advantages

  • Cost-effectiveness：Unlike phosphorescent materials, TADF materials rely entirely on organic materials, reducing dependence on expensive noble metals.

  • High Efficiency：Achieves nearly 100% IQE by harvesting both singlet and triplet excitons.

  • Color Purity：MR-TADF OLEDs offer narrowband emission, ideal for displays requiring vibrant and accurate colors.

  • Scalability：TADF materials can be processed using solution-based techniques like inkjet printing, enabling large-scale manufacturing.

 

Applications

  • Displays：TADF OLEDs are already used in high-resolution displays for smartphones, TVs, and wearable devices.

  • Lighting：Offers energy-efficient solutions for decorative and general-purpose lighting.

  • Specialized Applications：MR-TADF OLEDs are ideal for applications demanding precise color reproduction, such as augmented reality (AR) and virtual reality (VR) displays.

 

Conclusion

TADF OLED technology bridges the gap between cost, efficiency, and scalability, making it a highly promising next-generation OLED device technology. With further advancements in material design, such as MR-TADF emitters and novel donor-acceptor systems, TADF OLEDs are poised to redefine the boundaries of performance in the display and lighting industries.

 

Additional Reading

Deori, U., Nanda, G. P., Murawski, C., & Rajamalli, P. (2024). A perspective on next-generation hyperfluorescent organic light-emitting diodes. Chemical Science, 15(17739–17759).

Basyouni, M. Z., Radwan, M. F., Abdu, M. E., & Spring, A. M. (2024). Concise Review of TADF: Basic Principles, Material Design, Prospective Applications, and the Role of ROMP in Polymer Synthesis. Proceedings of International Exchange and Innovation Conference on Engineering & Sciences, 10, 597-601.

Konidena, R. K., & Lee, J. Y. (2019). Molecular Design Tactics for Highly Efficient Thermally Activated Delayed Fluorescence Emitters for Organic Light Emitting Diodes. The Chemical Record, 19(1499–1517).

Prabhu, K. C., & Naveen, K. R. (2023). Acceptor–donor–acceptor based thermally activated delayed fluorescent materials: Structure–property insights and electroluminescence performances. Materials Chemistry Frontiers, 8(769–784).

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