Illustration of a radical-based OLED emitting deep-red light.

Doublet Power: New Light-Emitting Diodes Shatter Efficiency Records

Q: How do radical-based OLEDs overcome the limitations of traditional OLEDs?

Radical-based OLEDs utilize a spin doublet emission process, whereas conventional OLEDs rely on singlet or triplet excitons. Radical emitters possess a singly occupied molecular orbital (SOMO), which enables selective hole injection into the HOMO and electron injection into the SOMO, forming a fluorescent doublet excited state and boosting light emission efficiency. This circumvents the efficiency limitations associated with traditional OLEDs, leading to higher performance.

Q: What efficiency levels have been achieved using TTM-3NCz and TTM-3PCz in radical-based OLEDs?

The development of radical-based OLEDs, specifically those incorporating TTM-3NCz and TTM-3PCz, has led to OLEDs with electroluminescence peaks at 710 nm and 703 nm, respectively. These OLEDs achieved maximum external quantum efficiency (EQE) values of 27% for TTM-3NCz and 17% for TTM-3PCz. These figures signify a breakthrough, suggesting near-100% internal quantum efficiency, surpassing previous achievements in deep-red and infrared LEDs.

Q: What are TTM-3NCz and TTM-3PCz, and how do they contribute to the performance of radical-based OLEDs?

TTM-3NCz and TTM-3PCz are luminescent radicals incorporating 3-substituted-9-(naphthalen-2-yl)-9H-carbazole (3NCz) and 3-substituted-9-phenyl-9H-carbazole (3PCz) to the core tris(2,4,6-trichlorophenyl)methyl (TTM) radical. When used in a 4,4-bis(carbazol-9-yl)biphenyl (CBP) matrix film, TTM-3NCz exhibits a photoluminescence quantum efficiency (PLQE) of (85.6±5.4)% at 707 nm, while TTM-3PCz shows a PLQE of (60.4±0.9)% at 695 nm.

Q: Why is vacuum deposition important in the manufacturing of OLEDs with TTM-3NCz and TTM-3PCz?

Vacuum deposition, a technique where materials are evaporated and deposited in a vacuum environment, is critical in the fabrication of OLEDs using TTM-3NCz and TTM-3PCz. During this process, the evaporation temperatures of TTM-3NCz and TTM-3PCz under vacuum remain below 473 K. Precise control of this process ensures the creation of high-quality, efficient devices. This process helps achieve the desired film properties and device performance.

Q: What are the potential future implications and applications of using doublet emission in radical-based OLED technology?

The utilization of doublet emission in radical-based OLEDs opens opportunities for brighter, more energy-efficient deep-red and infrared LEDs. These advancements can have implications for display technologies, leading to improved screen performance and reduced power consumption. Furthermore, the enhanced efficiency of infrared LEDs can benefit various applications such as remote controls, optical communication, and night vision systems, making these devices more effective and energy-efficient.

Nico Varela in Tech & Innovation September 2025 • 4 min read.

"Radical-based OLEDs unlock unprecedented performance in deep-red and infrared LEDs, paving the way for brighter displays and advanced lighting solutions."

Organic light-emitting diodes (OLEDs) are gaining traction as a key technology for displays and active lighting, offering lightweight and flexible solutions. While OLEDs are already used in some high-end products, reducing manufacturing costs while maintaining high performance is crucial for wider adoption.

A significant breakthrough has been achieved with the development of radical-based OLEDs, which utilize a spin doublet emission process. Unlike traditional OLEDs that rely on singlet or triplet excitons, these new devices circumvent efficiency limitations, leading to unprecedented performance.

By employing a luminescent radical emitter, researchers have created an OLED with a maximum external quantum efficiency of 27% at 710 nanometers. This represents the highest reported value for deep-red and infrared LEDs, opening up new possibilities for these technologies.

Doublet Emission: Bypassing Triplet Bottlenecks

Illustration of a radical-based OLED emitting deep-red light.

Conventional organic semiconductors rely on the recombination of electrons and holes occupying the highest occupied and lowest unoccupied molecular orbitals (HOMOs and LUMOs), resulting in the formation of singlet or triplet excitons. However, radical emitters possess a singly occupied molecular orbital (SOMO) in their ground state, giving them a spin-1/2 doublet. Under energetic grounds, both electron and holes occupy this SOMO level, light emission is not expected.

This new class of OLEDs achieves selective hole injection into the HOMO and electron injection into the SOMO, which leads to form a fluorescent doublet excited state with near-unity internal quantum efficiency. This strategic approach allows the creation of a fluorescent doublet excited state, boosting light emission efficiency.

TTM-3NCz and TTM-3PCz: New luminescent radicals with 3-substituted-9-(naphthalen-2-yl)-9H-carbazole (3NCz) and 3-substituted-9-phenyl-9H-carbazole (3PCz) to the core tris(2,4,6-trichlorophenyl)methyl (TTM) radical incorporated.
High PLQE Values: The photoluminescence quantum efficiency (PLQE) in solid 4,4-bis(carbazol-9-yl)biphenyl (CBP) matrix film (3.0 wt%) is (85.6±5.4)% and (60.4±0.9)% for deep-red emission in TTM-3NCz (707 nm) and TTM-3PCz (695 nm), respectively.
Vacuum Deposition: OLEDs using TTM-3NCz and TTM-3PCz as emitters were fabricated by vacuum deposition processing (pressure <6 × 10-7 torr). The evaporation temperatures of TTM-3NCz and TTM-3PCz under vacuum are below 473 K.

The resulting OLEDs, incorporating TTM-3NCz and TTM-3PCz, exhibit electroluminescence peaks at 710 nm and 703 nm, respectively, confirming their deep-red emission. Maximum EQE values of 27% for TTM-3NCz OLEDs and 17% for TTM-3PCz OLEDs suggest near-100% internal quantum efficiency, which exceeds previous achievements in deep-red/infrared LEDs.

Future Implications and Applications

This breakthrough in radical-based OLED technology holds significant promise for the future of displays and lighting. The high efficiency achieved through doublet emission opens doors for brighter, more energy-efficient deep-red and infrared LEDs.

Potential applications include advanced display technologies, improved infrared sensors, and innovative lighting solutions. Further research and development in this area could lead to widespread adoption of radical-based OLEDs in various industries.

While challenges remain in terms of manufacturing scalability and long-term stability, the remarkable performance of these novel OLEDs marks a major step forward in organic electronics.

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This article is based on research published under:

DOI-LINK: 10.1038/s41586-018-0695-9, Alternate LINK

Title: Efficient Radical-Based Light-Emitting Diodes With Doublet Emission

Subject: Multidisciplinary

Journal: Nature

Publisher: Springer Science and Business Media LLC

Authors: Xin Ai, Emrys W. Evans, Shengzhi Dong, Alexander J. Gillett, Haoqing Guo, Yingxin Chen, Timothy J. H. Hele, Richard H. Friend, Feng Li

Published: 2018-11-01

Everything You Need To Know

How do radical-based OLEDs overcome the limitations of traditional OLEDs?