New 'Fluorescent' Material Has Almost 100% Internal Quantum Efficiency

Dec 14, 2012
Tetsuo Nozawa, Nikkei Electronics
The TADF principle. Excitors in the triplet state (T1) are "promoted" to the singlet state by heat energy.
The TADF principle. Excitors in the triplet state (T1) are "promoted" to the singlet state by heat energy.
[Click to enlarge image]
Examples of the newly-developed materials
Examples of the newly-developed materials
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Examples of OLED panels made by using the new materials
Examples of OLED panels made by using the new materials
[Click to enlarge image]

The Center for Organic Photonics and Electronics Research (OPERA) of Kyushu University announced that it has developed a new OLED light-emitting material that is a fluorescent material and has an internal quantum efficiency of almost 100%.

Thus far, phosphorescent materials using rare metals have been the only materials with high internal quantum efficiencies. But the new material does not use a rare metal.

OPERA named the material "Hyperfluorescence" and announced its details on Nature magazine.

"It eliminates the need for phosphorescent materials," said Chihaya Adachi, professor at the university and project leader of OPERA.

OLED light-emitting materials can be classified into fluorescent and phosphorescent materials by the difference of light emission principle. Fluorescent materials are recombined (emit light) only when excitors go through a spin state called "singlet state." On the other hand, phosphorescent materials emit light not only when they are in the singlet state but also when they are in a spin state called "triplet state."

Because the ratio of the occurrences of the singlet and triplet states is 1:3, it has been considered that the maximum internal quantum efficiency of fluorescent materials is 25% and that of phosphorescent materials is 100%. The energy of fluorescent material's excitors in the triplet state is not used for light emission, and most of it is lost as heat.

This leads to the difference in the luminous efficiency of OLED device. Therefore, phosphorescent materials are more and more employed in the development of OLED displays and OLED lighting apparatuses. OLED devices whose luminous efficiencies are higher than 50lm/W are realized with phosphorescent materials expect for blue light-emitting materials.

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