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NTHU Researchers Develop the Third Generation OLED
A research team led by Professors Cheng Chien-hong and Liu Rai-shung of the Department of Chemistry, and Professor Lin Hao-wu of the Department of Materials Science and Engineering has successfully developed a new generation of ultra-high-performance organic light-emitting diode (OLED) using third generation diboron materials. In addition to reaching a record high efficiency of 38 percent, its production cost of this new material is estimated to be only one-fifth of that of second-generation OLEDs, and environmental pollution is also greatly reduced. This outstanding research achievement was recently featured in Nature Photonics, the top journal in the field of optoelectronics. The editors of the journal were impressed by this outstanding achievement and indicated that the efficiency of the OLED has made a new record, which is not only “a pride of NTHU” but also “a glory of Taiwan.”
 
OLEDs are light, thin, self-illuminating, colorful, and suited for planar surfaces, making them well suited for use in mobile phone screens, high-definition TVs, lighting, virtual reality, and augmented reality, and may even be suited for making transparent and flexible display screens like those seen in sci-fi movies. Prof. Liu said that the development of OLED panels is a highly competitive field with the main players being South Korea’s Samsung and LG, and China’s Everdisplay Optronics. By contrast, Taiwan is lagging behind in this area, and that’s what makes this recent breakthrough especially significant.
 
Prof. Cheng, who presided over the study, said that with the support of the Ministry of Science and Technology (MOST), the Tsing Hua team has been developing luminescent materials for more than 15 years, and with the recent addition of Professors Liu and Lin, who specialize in material design, component development, and advanced measurement technology, the research team finally achieved a breakthrough.
 
According to Cheng, most OLEDs currently on the market are mainly composed of fluorescent or phosphorescent materials, and the efficiency of first-generation fluorescent elements is only about 5%, and even though the efficiency of the second-generation of phosphorescent elements was raised to 20%, both require such precious metals such as iridium and platinum, which makes them expensive. Therefore, in recent years many laboratories focus on the development of thermally activated delayed fluorescence (TADF) materials, which cost less and are made of purely organic materials. Currently, the efficiency of TADF materials is comparable to that of second-generation phosphorescent materials, but it suffers from efficiency roll-off at high luminance.
 
To break such a bottleneck, the Tsing Hua team decided to work on developing low-cost diboron materials for use in OLED components. The new diboron material was synthesized and designed by postdoctoral researcher Wu Tien-lin, while another post-doc researcher, Min-jie conducted theoretical calculation and analysis of the material’s molecules. Then Dr. Chih-chun designed an optimized component structure for surmounting the external quantum efficiency limitations of traditional fluorescent and phosphorescent OLEDs. Next, Huang Pei-yun’s skill in component manufacturing and Tsu-yu’s expertise in optical measurement technology were used to successfully produced a high-efficiency OLED device with a luminous efficiency of 38 percent, and an efficiency roll-off of only 0.3 percent when the luminosity level reaches 1,000 cd/m2—a major breakthrough in the development of the next generation of pure organic luminescent materials.
 
Prof. Lin Hao-wu said that the rod-like molecular structure of diboron makes it possible to horizontally arrange the surface of the component in a thermal evaporation environment, reducing the refraction emission loss inside the component, thereby increasing the component’s efficiency. A variable-angle fluorescence measurement system set up by team member Chen-Cheng was used to confirm that up to 84 percent of the diboron material lies flat on the substrate. The Frontier Research Center on Fundamental and Applied Sciences of Matters headed by Prof. Liu is now working on the production process and extending the lifespan of OLEDs. Diboron is quite simple to synthesize and can be mass-produced, significantly reducing the cost of key luminescent materials used in OLEDs. This material design and its OLED application has already been patented in Taiwan and additional patents have been applied for in the United States, Japan, and China. It is estimated that it will be ready for commercial production within two years.
 

The green OLED developed at NTHU illuminating the school emblem.

The green OLED developed at NTHU illuminating the school emblem.


Prof. Cheng Chien-hong presenting the green and orange high-efficiency OLED.

Prof. Cheng Chien-hong presenting the green and orange high-efficiency OLED.


Members of the research team presenting their work at the MOST. From left to right: Liu Rai-shung, Senior Vice President Chen Sinn-wen, Wu Tien-lin, Prof. Cheng Chien-hong, and Prof. Lin Hao-wu.

Members of the research team presenting their work at the MOST. From left to right: Liu Rai-shung, Senior Vice President Chen Sinn-wen, Wu Tien-lin, Prof. Cheng Chien-hong, and Prof. Lin Hao-wu.


The structure and luminosity of diboron molecules.

The structure and luminosity of diboron molecules.

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