Idemitsu Kosan Co.,Ltd. has developed a new light emission system for organic light emitting diodes (OLEDs) using blue fluorescent materials that sets the world’s highest performance record for luminous efficiency beyond the conventional theoretical limit. The new system also successfully extends the lifetime of these OLED devices.
This achievement has been received the “Distinguished Paper Award”*1 at Display Week 2022, the world’s largest technical symposium and exhibition for emerging technologies in the global electronic display industry, held by the Society for Information Display (SID).
Summary of results
Generally, full-color displays are made up of the three primary colors: red, green, and blue. As such, OLED materials also need to generate each of these colors. Blue OLEDs in a full color display have larger electronic power consumption relative to green and red OLEDs. It is more difficult for blue OLEDs to achieve high luminous efficiency compared to OLEDs emitting red and green light.
In the present invention, Idemitsu succeeded in developing and putting into practical use OLED technology with higher luminous efficiency and longer lifetime compared with conventional technologies by laminating two blue materials. Idemitsu attained high efficiency (EQE*2> 14%) in the blue OLED devices by separating the region that causes charge recombination*3 and utilizing TTF*4 in the light emission process of the fluorescent OLED*5, thereby suppressing light emission loss. This improvement enables energy savings as well as longer lifetime for products using OLED technology. As such, the present invention will contribute to realize more environmentally-friendly display products in society.
Summary of Performance
System: Blue fluorescent OLED using the laminated emission layer
LT95*6: Over 400 hours (driving condition under current density of 50 mA/cm2)
EQE: 14% (driving condition under current density of 10 mA/cm2)
Chromaticity: (0.14, 0.08) (based on CIE1931 color coordinates)
Receiving the “Distinguished Paper Award” at Display Week 2022
The present invention has been received for the “Distinguished Paper Award” in the OLED technology category at Display Week 2022, which was held in San Jose, California, United States from May 8-13, 2022.
Idemitsu intends to continue contributing to international markets through the introduction of outstanding products and unique technologies created by innovative research and development and intellectual property activities.
- *1
- Distinguished Paper: “Realization of Ultra-High Efficient Fluorescent Blue OLED” (Satomi Tasaki, Kazuki Nishimura, Hiroaki Toyoshima, Tetsuya Masuda, Masato Nakamura, Yuki Nakano, Hiroaki Itoi, Emiko Kambe, Yuichiro Kawamura, Hitoshi Kuma) Journal of the Society for Information Display, Volume 30, Issue 5, pages:441-451 (2022) https://sid.onlinelibrary.wiley.com/doi/epdf/10.1002/jsid.1127
- *2
- EQE: Abbreviation for External Quantum Efficiency. An index showing the percentage of current entering a device that is emitted from the device as light. A larger value means a higher luminous efficiency of the OLED.
- *3
- Charge recombination zone: The zone in which holes (positive carriers) and electrons (negative carriers) that are injected from the anode and the cathode, respectively, collide and generate a high-energy state of the organic materials in the device (excitons). On the other hand, a high carrier density can easily lead to interaction with the excitons and the carriers, thereby quenching the excitons.
- *4
- TTF: Abbreviation for Triplet-Triplet Fusion. A phenomenon by which singlet excitons are generated through the collision of triplet excitons. Device efficiency can improve by diverting triplet excitons, which are not used in fluorescent OLEDs, into luminescence.
- *5
- Fluorescent OLED: An OLED in which singlet excitons are used for luminescence. The organic material in the device transitions into a high-energy state (excitons) through electrical excitation. Two types of organic excitons are generally known, one is the singlet exciton and the other is the triplet exciton.
- *6
- LT95: The duration from initial brightness to a 5% reduction in brightness under device operation using a constant current density.
