Organic Electro-Luminescence

In-house development including OLED material design and fabrication, and panel prototyping.
Aiming for pioneering high-performance OLED displays

Now, OLED displays are the mainstream of displays as well as LCDs, and have been actively developed to pursue higher performance: high efficiency, long lifetime, high resolution, and wide color gamut. To realize high-performance OLED displays, we conduct all the processes in-house including OLED material design and fabrication, and panel prototyping.

First, molecules are designed and their physical properties are predicted through AI and material analysis simulations using a supercomputer; organic synthesis is performed; light-emitting devices are fabricated for testing; then, their characteristics are evaluated. In all the steps, we pursue the optimal materials and devices for displays, leading to fabrication of high-performance OLED display prototypes.

▲Photoluminescence demonstrated in solution

▲OLED (Left: red, Right: green)

OLED materials and devices development
―Higher-Brightness and Longer-Life Technology―

SEL’s original technology, ExTET®

ExTET, which was originally developed by SEL, is the technology enabling higher efficiency, lower driving voltage, and a longer lifetime of OLED displays. In a phosphorescent OLED, the excitation energy of a host material is transferred to a phosphorescent material (guest material) in a light-emitting layer, so that the phosphorescent material emits light. Conventionally, this energy transfer would cause energy loss to adversely affect the emission efficiency, driving voltage, and lifetime. SEL developed an energy transfer mechanism in which an exciplex formed by combination of an electron-transport material and a hole-transport material is used as a medium for energy transfer to a phosphorescent material, and applied for a patent for this mechanism in 2011. We named this technology Exciplex-Triplet Energy Transfer (ExTET)[1]. ExTET successfully cut the energy loss and thereby solved the problems of the emission efficiency, driving voltage, and lifetime of phosphorescent OLEDs at a time[2],[3]. Being essential for OLED displays, ExTET is a fundamental technology used in the green- and yellow-light-emitting layers of commercially available OLED displays, and sometimes also used in red-light-emitting layers.

▲Conceptual diagram

▲Basic mechanism of ExTET

>>Press Release “Semiconductor Energy Laboratory Co., Ltd. Validity of important patent for OLED technology was upheld”

[1] S. Seo et al., “Exciplex-triplet energy transfer: A new method to achieve extremely efficient organic light-emitting diode with external quantum efficiency over 30% and drive voltage below 3V,” Jpn. J. Appl. Phys., 53, 042102-1 (2014).  DOI: 10.7567/JJAP.53.042102
[2] T. Takahashi et al., “Emission mechanism in phosphorescent and fluorescent OLED utilizing energy transfer from exciplex to emitter,” J. Soc. Inf. Disp., 24(6), 360 (2016).
[3] S. Seo et al., “Recent development of organic light-emitting diode utilizing energy transfer from exciplex to phosphorescent emitter,” Proc. of SPIE, 9941, 99410J-1 (2016).

TTA increases emission efficiency of fluorescent device

In a current-excitation device, there is a 25 % probability (internal quantum efficiency) of producing a singlet exciton leading to fluorescence and 75 % probability of producing a triplet exciton. Thus the emission efficiency of a fluorescent device is lower than that of a phosphorescent device but if an increase in the probability of producing a singlet exciton by some method would increase the emission efficiency. One method is TTA, which is a phenomenon where a singlet exciton is formed in a light-emitting layer by mutual interaction of triplet excitons. We have found a device structure to enhance the probability of producing TTA and developed a fluorescent device with high emission efficiency[4],[5].

▲increase in emission efficiency of fluorescent device by TTA

▲Energy diagram of TTA

[4] T. Suzuki et al., “Highly efficient long-life blue fluorescent organic light-emitting diode exhibiting triplet-triplet annihilation effects enhanced by a novel hole-transporting material,” Jpn. J. Appl. Phys., 53(5), 052102 (2014).   DOI: 10.7567/JJAP.53.052102
[5] N. Hashimoto et al., “Investigation of Effect of Triplet-Triplet Annihilation and Molecular Orientation on External Quantum Efficiency of Ultrahigh-Efficiency Blue Fluorescent Device,” SID Symp. Dig. Tech. Pap., 47, 301 (2016).

While assessing the market needs and trends, we have been developing various other OLED materials and devices in our laboratory to pursue higher performance OLED displays[6],[7],[8].

[6] Y. Takita et al., “Highly Efficient Deep-Blue Fluorescent Dopant for Achieving Low-Power OLED Display Satisfying BT.2020 Chromaticity,” SID Symp. Dig. Tech. Pap., 49(1), 138 (2018).  DOI: 10.1002/jsid.634
[7] T. Ishimoto et al., “Ultralong-Life Deep-Blue OLED Device Achieved by Controlling the Carrier Recombination-Site,” SID Symp. Dig. Tech. Pap., 236 (2021).
[8] T. Watabe et al., “Ultrahigh-Performance Blue Fluorescent OLED Achieving Efficiency over 250 cd/A/CIEy Utilizing Organic Carrier-Transport Material with Low Refractive Index,” SID Symp. Dig. Tech. Pap., 247 (2021).

OLED display development

Jump to OLED Display page

Turning on the light when the room is dark.
Such simple daily actions give us hints for invention.

OLED Lighting Panel

OLED lighting has low power consumption and long life, and also has excellent color rendering properties which produce light that is close to natural light. It is also favorable environmentally and in design ability, as it is mercury-free, has a surface light source, and is thin, light, and flexible. We are developing light boards[9] and flexible lighting[10] with the goal of practical application, and we are also striving to improve power efficiency, lifetime, and color rendering properties of OLED lighting, with the goal of popularizing OLED lighting.

[11] S. Seo et al., “Highly Efficient Long-Lived Blue Fluorescent OLED Achieving External Quantum Efficiency over 8% and Its Application to OLED Lightings,” SID Symp. Dig. Tech. Pap., 41, 1837 (2010).
[12] N. Ohsawa et al., “Large-Sized Flexible Lighting with Highly Efficient OLEDs,” SID Symp. Dig. Tech. Pap., 44, 923 (2013).

* ExTET is a registered trademark of Semiconductor Energy Laboratory Co., Ltd. (Japanese trademark registration No. 5666910).