Recently, Japan’s largest organic Optoelectronics Research Center (OPERA) from Kyushu University announced the development of a new type of OLED chip with 100% internal quantum efficiency. Previous materials with high internal quantum efficiency are limited to those phosphorescent materials using rare metals. OPERA named this material as “Hyper-fluorescence”.
OLED light-emitting materials can be divided into fluorescent material and phosphorescent material based on different light-emitting principles. Fluorescent material can combine (emit light) when excitons in a doublet spin state. In addition to a doublet spin state, phosphorescent material can realize light emitting also through a triplet spin state. Normally, the double spin state and triplet spin state occurs in the ratio of 1:3. Thus, the maximum quantum efficiency of fluorescent materials is about 25% and the maximum phosphorescent materials can reach up to 100%. In the fluorescent materials, the energy of triplet excitons generally cannot be converted to optical energy (light emitting) but lost as heat.
This phenomenon is obvious in OLED components with different luminous efficiencies. Thus in the development of OLED display and latterly LED Tunnel Light lighting applications, the utilization of phosphorescent materials increased continuously. OLED chip with a luminous efficiency of 50% can be achieved by using phosphorescent materials, as well as blue light-emitting materials. But phosphorescent materials still have a number of issues need to be solved: a. phosphorescent materials contain rare metals, which are very expensive; b. Universal Display technology (UDC) controls most of related patents; c. blue phosphorescent materials have relatively short service life, not practical.
In recent years, scientists found several materials with internal quantum efficiency of more than 25%, in spite that they all belong to fluorescent materials. Andaman Research Office of OPERA is very concerned about this phenomenon, launching a series of studies to materials that can help to improve the luminous efficiency and naming one of the light-emitting principles as “thermal activity delayed fluorescence” (TADF).
TADF can send out light only when excitons in the doublet spin state. Based on this feature, they belong to fluorescent materials. But after heating, the triplet excitons will transform into doublet state. Thus it is possible for all excitons in this kind of materials emit light during the combination. Andaman Research Office has strengthened the study effort of OLED chip with 100% internal quantum efficiency.