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[IMID 2018] 청색 TADF와 hyperfluorescence, 효율과 수명 두 마리 토끼 모두 잡을 수 있을까

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8월 31일 부산 BEXCO에서 열리고 있는 IMID 2018에서 Kyulux의 CEO, Junji Adachi는 기존의 형광재료 host와 dopant에 TADF dopant를 첨가하는 hyperfluorescence의 성능들을 공개했다.

Junji Adachi가 공개한 노란색 hyperfluorescence의 색좌표는 (0.49,0.50), 반치폭은 76 nm, 1,000 nit 기준 EQE는 15.7%, 1000 nit 기준 LT50은 6만 2천시간이며, 녹색 hyperfluorescence의 색좌표는 (0.28,0.65), 반치폭은 31 nm, 1000 nit 기준 EQE는 20.6%, 1,000 nit 기준 LT50은 4만 8천시간이다.

이 자리에서 Junji Adachi는 현재 개발 중인 청색 hyperfluorescence의 성능도 공개했는데, 최대 발광 파장은 470 nm, 1000 nit 기준 EQE는 22%, 750 nit 기준 LT50은 100시간이라고 밝혔다. 특히, 2018년 상반기부터 청색 hyperfluorescence의 성능이 빠른 속도로 향상되기 시작했다며 앞으로 성능이 더욱 더 향상 될 것으로 기대했다.

이어진 발표에서 CYNORA의 Dr. Georgios Liaptsis는 현재 개발 중인 진한 청색(deep blue)을 설명하며 파장은 460 nm, CIEy는 0.15 이내가 되야 한다고 강조했다. 연한 청색(sky blue)로 갈수록 수명이 길어지는 특징이 있는데, CYNORA는 진한 청색으로 연한 청색만큼의 수명을 가질 수 있도록 연구를 진행하고 있다고 설명하며 성능을 공개했다.

현재 모든 OLED application의 청색은 형광 청색이 사용되고 있다. 청색 TADF나 청색 hyperfluorescence가 상용화 되어 기존의 형광 청색보다 더 개선 된 효율과 수명을 보여줄 수 있을지 귀추가 주목된다.

The 4th Generation Emitting Material, Hyperfluorescence

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Thermally activated delayed fluorescence(TADF), still under development to complement OLED emitting materials insufficient as both fluorescence and phosphorescent materials, takes time to be commercialized at the present stage. Even Kyulux considered the most advanced company in terms of TADF technology hasn’t yet to commercialized TADF dopant suitable for display.

Adachi, CTO of Kyulux said the unprepared TADF host material is an obstacle to the commercialization of TADF, so the full width at half maximum of emitting peak is too wide to be applied to display. To solve this problem, the 4th generation hyperfluorescence is under development to commercialize the TADF material.

 

<Kyulux CTO Adachi>

 

 

Hyperfluorescence aims at having the effect of a phosphorescent material by adding TADF dopant to existing fluorescence host and dopant.

 

 

<Hyperfluorescence Effect>

 

This effect has a structure that can solve both the full width at half maximum of TADF and the low brightness of fluorescence materials as seen in the above figure, Adachi emphasized.

 

<Hyperfluorescence vs General fluorescence>

 

 

As seen in the above photo, Kyulux’s OLED made of general green fluorescence material and OLED made of hyperfluorescence by adding TADF to this material have a distinct difference on the same substrate.

Kyulux’s goal is to commercialize hyper fluorescence by 2017. Its target is PMOLED.

International TADF Workshop Opening

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<Source : 2nd International TADF Workshop>

The International Workshop on the third generation of light emitting material technology, TADF (Thermally Activated Delayed Fluorescence) technology, which links first-generation fluorescent material technology and second-generation phosphorescent material technology, will be held at Kyushu University from July 19 to 21, 2017

In order to push the LCD, which is now the flagship product of the display market replacing the cathode-ray tube completely in the market, it is necessary to have a high-efficiency, low-cost OLED that can be used in mid/low-priced products. A solution to solve both high efficiency and low cost depends on the commercialization of retarded fluorescent materials.

Currently, the light emitting materials are classified into red, green, and blue host materials and dopant materials of respective colors. Among these materials, red and green use phosphorescent materials that internal efficiency is theoretically 100%, but blue materials still use fluorescent materials that internal efficiency is only 25%. Due to the limit of blue material efficiency, large OLED panels for TV have a structure in which blue layers are laminated twice, so material cost is very high.

TADF is the material that is being developed to overcome the limitations of current OLED emissive materials.

In the International TADF Workshop, headed by Professor Adachi of Kyushu University, who brought TADF technology to the world for the first time, worldwide experts of third-generation OLED lighting material development gather. Professor Adachi implied that the interest in TADF is getting hotter around the world looking from that 3 years later he published a TADF thesis for the first time in 2012 at Kyushu university approximately 120 papers published worldwide in 2015 and there are more than 200 papers published in 2016.

Professor Adachi said that the meaning of the TADF Workshop this time is to discuss with experts about the current TADF reach and future development.