Milestone-Proposal:White Organic LED, 1993

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Docket #:2024-35

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To the proposer’s knowledge, is this achievement subject to litigation? No

Is the achievement you are proposing more than 25 years old? Yes

Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes

Did the achievement provide a meaningful benefit for humanity? Yes

Was it of at least regional importance? Yes

Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes

Has the IEEE Section(s) in which the plaque(s) will be located agreed to arrange the dedication ceremony? Yes

Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes

Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes

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Year or range of years in which the achievement occurred:

1993-1995

Title of the proposed milestone:

Realization of White Organic Light Emitting Device (OLED), 1993

Plaque citation summarizing the achievement and its significance; if personal name(s) are included, such name(s) must follow the achievement itself in the citation wording: Text absolutely limited by plaque dimensions to 70 words; 60 is preferable for aesthetic reasons.

In 1994, Junji Kido realized the white organic light emitting device (OLED) for the first time and succeeded in improving brightness and lifetime by employing a tandem structure. Such white OLEDs have been used to realize general lighting panels and large-size color displays combined with color filters. For his contributions to the display industry, he was awarded the Karl F. Braun Prize by the Society for Information Display in 2015.

200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.

OLEDs are light-emitting devices similar to the conventional inorganic LEDs. Green OLED display was first commercialized in 1997. Since then, various small-size OLED displays have been developed, and today used in smartphones and other mobile applications. Junji Kido is the pioneer in the development of white OLEDs. The first white OLED was realized by using polymer emitter layer dispersed with several kinds of fluorescent dyes. The second white OLED was fabricated by successive vacuum deposition of blue, green and red emitter layers so that the emission color becomes white. The results were so original and impressive that the paper was reported by business journals like "the Wall Street Journal" and "Business Week". Wall Street Journal (May 10, 1995) cited his work entitled "Japanese Light Researcher May Turn LED into Gold". He also invented tandem OLEDs for long lifetime at high luminance level. OLEDs of this type exhibit high current efficiency and require extremely low driving current, which improve the drive-lifetime. White OLEDs, having tandem structures, have been used for white OLED panels for general lighting. Today, it also becomes an essential technology for large-size OLED displays combined with RGB color filters. Lumiotec Inc. was founded as a joint venture company by Junji Kido, Mitsubishi Heavy Industry, Toppan Printing, Rohm, and Mitsui Company to manufacture white OLED panels for lighting in 2008 and started manufacturing panels in 2011.

IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.

IEEE Electron Device Society

In what IEEE section(s) does it reside?

IEEE Sendai section

IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:

IEEE Organizational Unit(s) paying for milestone plaque(s):

Unit: IEEE Sendai section
Senior Officer Name: Hiroaki Muraoka

IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: IEEE Sendai section
Senior Officer Name: Hiroaki Muraoka

IEEE section(s) monitoring the plaque(s):

IEEE Section: IEEE Sendai section
IEEE Section Chair name: Hiroaki Muraoka

Milestone proposer(s):

Proposer name: Hsinglin Lan
Proposer email: Proposer's email masked to public

Proposer name: Chiaki Ishikawa
Proposer email: Proposer's email masked to public

Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.

Street address(es) and GPS coordinates in decimal form of the intended milestone plaque site(s):

Frontier center for organic materials, Yamagata University, 4-3-16 Jonan, Yonezawa City, Yamagata, 992-8510, Japan.

GPS coordinates: 37.8999472,140.1019157

Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.

Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. The Frontier Center for Organic Materials at Yamagata University is where Junji Kido's current office and lab space are located. He served as the director there from 2016 to 2024. There are panels and exhibits showcasing Mr. Kido's achievements there.

Are the original buildings extant?

No

Details of the plaque mounting:

It will be displayed in the exhibition hall.

How is the site protected/secured, and in what ways is it accessible to the public?

The Frontier Center is equipped with security cameras and is locked on weekends, requiring a card key for access.

Who is the present owner of the site(s)?

Yamagata University

What is the historical significance of the work (its technological, scientific, or social importance)? If personal names are included in citation, include detailed support at the end of this section preceded by "Justification for Inclusion of Name(s)". (see section 6 of Milestone Guidelines)

Justification of Name in Citation

Junji Kido's achievements in the invention of the white OLED are outlined in the following four sections:

1. The Beginning of Research on Rare Earths, 2. The Inception of White Organic LEDs, 3. The Development of Tandem OLED Technology with Multistage OLED Elements, and 4. Current Activities

The Beginning of Research on Rare Earths

During his graduation research at Waseda University, Professor Tsuchida, Kido's supervisor, suggested he study rare earths, leading Kido to embark on this path. It began as a pun but turned out to be fateful. Using rare earths as model materials, Kido's graduation research focused on creating an ion exchange resin to collect rare earths successfully. After graduating from Waseda University in 1984, Tsuchida introduced him to the laboratory of Professor Yoshiyuki Okamoto at the Graduate School of Polytechnic University in New York, renowned for its polymer research. There, Kido studied the bonding reaction between polymers and rare earth metal ions. He synthesized polymers and measured their luminescence characteristics, inspired by the plastics containing rare earth metal complexes in the Okamoto laboratory. Motivated by past papers, Kido discovered similar research by Professor M. Pope of New York University. In 1963, it was found that a single crystal of anthracene (C₁₄H₁₀) emitted light when a DC voltage was applied. Professor Okamoto, who had previously taught at New York University, had crafted an anthracene single crystal for Professor Pope. Consequently, Kido was introduced to Professor Pope by Professor Okamoto. Although Kido conducted luminescence experiments with a rare earth metal complex during his stay in the United States, it never glowed. Upon Tsuchida's recommendation, Kido returned to Japan in 1989 and became an assistant in the Department of Polymers at Yamagata University's Faculty of Engineering.

[3] J.Kido, M.Kimura and K.Nagai, “Multilayer White-Light-Emitting Organic Electroluminescent Device,” Science, 267, pp.1332-1334 (1995).

After returning to Japan, Kido came across a paper on OLED emission written by C.W. Tang of Eastman Kodak. Tang used an aluminum complex in his experiments, but the emission spectrum was broad, and the light's purity was not very high. Kido, knowing that rare earth complexes had a sharper emission spectrum than aluminum complexes, was convinced that an organic EL device using rare earth complexes could produce beautiful light. Despite his conviction, Yamagata University lacked the experimental equipment. Kido borrowed equipment from a domestic company and conducted experiments at Brookhaven National Laboratory in the United States during university holidays. These efforts culminated in 1990 when he finally developed an OLED device that emitted light and published a paper.

The Inception of White Organic LEDs

In 1993, Kido had already succeeded in producing blue organic EL (Electroluminescence) light using polymer materials. He then instructed his students to conduct experiments to achieve red OLED luminescence. In this experiment, a blue polymer organic material was mixed with a small molecule red dye to produce red OLED light emission. It was known that OLEDs emit light at the color of the dye with the lowest energy level, even when various dyes are mixed.

In the experiment that Kido instructed, two types of dyes—blue and red—were mixed, with the expectation of obtaining a red light of low energy levels. However, when Kido himself applied electricity to the OLED element brought by the student, it glowed whitish-pink instead of red.

When the three colors of red, green, and blue, which are considered the three primary colors of light, are mixed, it should result in white light. However, in the case of OLEDs, even if the three colors are mixed, they do not produce white light but instead become red. This had been the norm in the OLED world up to that point.

The color of the light emitted by OLEDs is determined by the high energy level of each dye. For example, the excitation energy level of blue is about 2.8 eV (electron volt), with a wavelength of about 440 nm. The excitation energy level of green (wavelength about 550 nm) is lower than that of blue, at about 2.3 eV, and the excitation energy level of red (wavelength about 700 nm) is even lower, at about 1.8 eV. When pigments of different emission colors are mixed, the excitation energy at the higher level is transferred to the lower energy level. Therefore, when blue, green, and red pigments are mixed, the high excitation energy of the blue dye first moves to the green energy level, then to the red energy level, and finally only the red emission with the lowest energy level occurs.

In other words, no matter how many types of dyes are mixed, the excitation energy is eventually transferred to the energy level of the dye with the lowest energy level, and the emission of light corresponds to that energy level. Hence, in the OLED world, it was believed that even if separate emissions of blue, green, and red existed, it was impossible to emit white light by mixing the three colors.

However, the OLED panel brought by the students glowed whitish-pink instead of red. Seeing this, Kido jumped up and down with joy. The whitish-pink glow in this "failed experiment" indicated that the amount of red dye was too small, so not all the electrons at the blue energy level transferred to the red energy level. Some of them emitted blue light, resulting in a whitish-pink color overall.

With this knowledge, the next steps were quick. When a small amount of green pigment was added to a mixture of blue and red pigments, genuine white light emission was achieved instead of pink, as expected. This marked the successful emission of the world's first white OLED light in 1993.

Technological Development of Tandem OLED with Multi-Stage OLED Elements

Kido collaborated with Aimes in Fujisawa City (Kanagawa Prefecture) on the research and development of multi-stage OLED elements. This collaboration led to the successful development of the world's first organic EL element with two light-emitting units, which was announced at the Japan Society of Applied Physics in March 2002. Kido stated, "The internal quantum efficiency exceeds 100% for the first time in the world," astonishing the attendees. Internal quantum efficiency is the efficiency at which electrons injected from the electrode are converted into photons. Although there is ongoing debate about whether the internal quantum efficiency truly exceeds 100%, the current effect is almost proportional to the number of stages stacked.

Additionally, Kido and Aimes jointly developed an organic EL element with three stacked light-emitting layers. The results of this work were presented in "Applied Physics" in September 2002 and at the "International Display Conference SID" in Baltimore, USA, in May 2003.

[6] http://www.universaldisplay.com/

[7] Kido, et al., "High-Quantum Efficiency Organic EL Devices with Charge Generation Layers," Proceedings of the Japan Association of Applied Physics, 27p-YL-3, p.1308, March 2002 (2002).

[9] Nakata, et al., "Multiphoton-emission organic EL devices with charge transfer complexes as charge generation layers," Proceedings of the Japan Association of Applied Physics, 27a-ZL-12, p. 1165, September 2002 (2002).

[10] J.Kido and A.Yokoi, “High efficiency organic EL devices having charge generation layers,” Digest 27.1, pp.964-965, SID 2003, (2003).

[11] A.Yokoi and J.Kido, “Multiphoton organic EL device having charge generation layer,” Digest 27.5L, pp.979-981, SID 2003, (2003).

In this way, Kido's pioneering tandem OLED technology, a multi-stage OLED element known as a multi-photon emission device (MPE), is set to become the mainstream technology for OLED panels in the future.

Current Activities

In March 2003, Yamagata Prefecture launched the "Yamagata Organic Electronics Valley" concept with Kido as the project leader, aiming to create an industry through the accumulation of organic electronics-related industries. The Organic Electronics Laboratory was established in Yonezawa as the core of this project, with Kido serving as its director. This seven-year project, costing 4.3 billion yen, consists of three development rooms: the manufacturing process development room, the product development room, and the organic device development room.

In November 2003, the institute began its activities as a grounded research institute to strengthen the technological capabilities and competitiveness of local companies, develop human resources for engineers, create new products, and provide manufacturing workshops (rental labs). The participation fee for companies within the prefecture is 2 million yen per year, and for companies outside the prefecture, it is 5 million yen per year. Either way, it allows participation in joint research at a low cost, and currently, 20 companies are participating in joint research. Through these collaborations with companies both inside and outside the prefecture, the institute supports application development, product prototyping, and commercialization.

Historical significance

Background

In 1987, Tang and colleagues at Eastman Kodak reported an OLED that emitted light from a green n-type emitting layer. Subsequent reports included devices emitting orange, red, and blue light.

Realization of White Organic Light Emitting Device (OLED)

Mechanism of Organic Light Emitting Device

The basic structure of an OLED resembles a sandwich, with p-type and n-type organic semiconductor thin films placed between two electrodes—an anode and a cathode. Generally, the anode is formed by depositing a transparent electrode called ITO (Indium Tin Oxide) onto a transparent substrate such as glass. From this anode, positively charged holes are injected into the p-type organic semiconductor layer. In contrast, the cathode does not need to be transparent and is therefore composed of metals such as aluminum or silver, which inject negatively charged electrons into the n-type organic semiconductor layer. The injected holes and electrons eventually reach the organic emissive layer, where their recombination excites the organic molecules, thereby generating light. By using blue, green, and red emissive materials, organic EL devices that emit each of these colors can be obtained. Furthermore, as proposed by Kido and colleagues, mixing or stacking these blue, green, and red emissive materials can blend the colors to produce white emission.

Realization of White Organic Light Emitting Device (OLED)

Regarding white emission, achieving it required mixing different emission colors, which meant that dyes with different emission wavelengths needed to emit light simultaneously. However, the challenge lay in the fact that dyes with different emission colors had different excitation energy levels, resulting in only the dye with the lowest excitation level emitting light. Kido and his team's white-emitting OLED was groundbreaking in that it achieved what seemed like an impossible task: producing white light. This accomplishment was highly significant, as it suggested that OLED could not only be used for displays but also serve as white light sources for general lighting. Additionally, it demonstrated that combining white light with color filters could enable easy colorization for full color displays, further elevating interest in OLED technology.

Social Impact of the Realization of White Organic Light Emitting Device (LED)

(a) Today, white OLED has not only been partially commercialized as lighting panels, but is also employed in large-size displays and small VR displays. In these large and small displays, it is not possible to separately deposit blue, green, and red elements using a shadow mask. Instead, a white OLED combined with a color filter is used to achieve the desired colors. For large-size displays, OLED TVs have been commercially produced in sizes up to 97 inches. In VR applications, products like Apple’s Vision Pro have already adopted this technology, and further developments are anticipated in the future.

(b) The OLED panel market size is estimated to reach USD 51.63 billion in 2024 and is forecast to grow to USD 95.93 billion by 2029, representing a CAGR of 13.19% during the forecast period from 2024 to 2029.

(c) The invention of OLEDs has had beneficial impacts on humanity in a variety of ways. Some key examples are listed below. 1.High-Quality Image Display: Since OLED displays are self-emissive, they do not require a backlight, enabling deep blacks and high contrast ratios. As a result, images and videos appear clearer and more natural, enhancing the viewing experience across a wide range of devices such as televisions, smartphones, tablets, and monitors. 2.Energy Savings and Reduced Environmental Impact: Compared to traditional LCDs, OLED panels often consume less power, thereby reducing their environmental footprint. Additionally, their ability to be made thin and lightweight helps lower energy consumption during transportation and installation. 3.Flexible, Lightweight Designs: Because OLEDs use organic materials, it is possible to create bendable, flexible displays and ultra-thin panels. This advancement has led to innovative products and applications, including foldable smartphones, rollable televisions, and wearable devices. 4.Versatile Applications (including Lighting): OLEDs are not limited to display technology. Their ability to produce a uniform light source across the entire surface makes them suitable for lighting applications as well. They can provide soft, warm illumination with minimal glare, making them valuable in various fields such as residential and automotive lighting, as well as decorative and design-oriented illumination. Taken together, the invention and development of OLEDs have improved quality of life, promoted energy efficiency, and enabled innovative product designs, delivering multifaceted benefits to society.

What obstacles (technical, political, geographic) needed to be overcome?

Obstacles to be overcome

Before achieving white OLEDs, Junji Kido successfully developed an n-type organic semiconductor with a large energy gap (TAZ)[1]. This groundbreaking material allowed p-type organic materials, which had previously been unsuitable for use as emitting layers, to emit light when TAZ was used. Building on this, Kido achieved blue-violet emission by pioneering a device fabrication method in which a p-type, blue-violet-emitting polymer material (PVK) was coated via solution processing, and TAZ was deposited via vacuum evaporation [2]. To obtain the primary emission colors needed for information displays—blue, green, and red—Kido dispersed a small amount of blue dye in PVK. Through the transfer of excitation energy from PVK to the dye, he succeeded in achieving pure blue emission. Following this, he achieved green emission. However, during the fabrication of red-emitting devices, he observed a whitish-pink light, which appeared as a mixture of red and blue emissions. This led him to hypothesize that when dyes were dispersed in minute amounts, the transfer of excitation energy might not fully occur. In such cases, if multiple dyes with different emission colors were dispersed, each dye could emit light, resulting in mixed colors and potentially white light. Acting on this idea, Kido dispersed trace amounts of blue, green, and red fluorescent dyes into PVK and fabricated a device. As he predicted, the device emitted white light [3]. At the time, the prevailing belief was that when multiple fluorescent dyes were present, excitation energy would transfer entirely to the material with the smallest energy gap, leading to red emission in this case. This breakthrough shattered conventional understanding, marking a pivotal moment of innovation.

What features set this work apart from similar achievements?

features set this work apart from similar achievements

At the time, OLEDs were characterized by low efficiency and short lifetimes, and research efforts were generally focused on enhancing their performance for practical application. Kido, as a chemist, not only worked on developing emission materials and n-type and p-type carrier transport materials but also conducted research on device structures aimed at improving performance. They devised innovative methods for performance enhancement, such as reducing driving voltage through chemical doping techniques for n-type and p-type materials, as well as developing electrode interface layer materials. Among these achievements, the white-emitting OLED stood out for its exceptional originality, as it successfully realized white emission—a feat previously considered impossible. As highlighted by The Wall Street Journal, this breakthrough had a significant impact on the industry, underscoring its far-reaching implications.

Why was the achievement successful and impactful?

why the achievement was successful and impactful, and be sure to briefly incorporate this in the citation

After Kido achieved the world's first white emission using solution-processable polymer materials, he proceeded to fabricate a blue-emitting device using a blue p-type material (TPD) with layers deposited exclusively by vacuum evaporation. The device structure was anode/TPD/TAZ/cathode. However, during this process, the driving voltage was unusually high, likely due to the low electron mobility of the n-type material TAZ. To address this, he fabricated a device using Alq, an n-type material widely used at the time and known for its green emission and presumed higher mobility than TAZ. The device structure was anode/TPD/TAZ/Alq/cathode. By thinning the TAZ layer to lower the driving voltage as much as possible, he found that if the TAZ layer was too thin, not only TPD but also Alq emitted light, resulting in blue-green emission. Kido then hypothesized that by dispersing a red-emitting dye into part of the Alq layer, the device could emit blue, green, and red light, which would mix to produce white light. When he fabricated such a device, it emitted beautiful white light as predicted. This was the world's first white-emitting device fabricated via vacuum evaporation [4]. The result was achieved by controlling the diffusion of charge carriers and excitons through the TAZ hole-blocking layer. Subsequently, Kido focused on enhancing the performance of white-emitting devices produced by vacuum deposition, eventually leading to their practical application.

Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.

Bibliography

References

[1] J. Kido, C. Ohtaki, K. Hongawa, K. Okuyama, K. Nagai. 1,2,4-Triazole Derivative as an Electron-Transport Layer in Organic Electroluminescent Devices. Japanese Journal of Applied Physics Part 2-Letters 32, L917-L920 (1993).

[2] J. Kido, K. Hongawa, K. Okuyama, K. Nagai. Bright Blue Electroluminescence from Poly(N-Vinylcarbazole). Applied Physics Letters 63, 2627-2629 (1993).

[3] J. Kido, K. Hongawa, K. Okuyama, K. Nagai. White Light-Emitting Organic Electroluminescent Devices Using the Poly(N-Vinylcarbazole) Emitter Layer Doped with 3 Fluorescent Dyes. Applied Physics Letters 64, 815-817 (1994).

[4] J. Kido, M. Kimura, K. Nagai. Multilayer White Light-Emitting Organic Electroluminescent Device. Science 267, 1332-1334 (1995).

Patents

[1] Electroluminescent Device Based on Organometallic Membrane, T. Skotheim, Y. Okamoto and J. Kido. US Patent, 5128587, 1992.

[2] Organic Electroluminescent device, J. Kido. US Patent, 5834130, 1998.

[3] Organic Electroluminescent Devices, J. Kido and T. Mizukami. US Patent, 6013384, 2000.

News and Magazine

[1] Wall Street Journal, May 10, 1995 "Japanese Lighting Researcher Hopes to Turn LED into Gold"

[2] Science, Vol.310, 1762, 2005 "Organic LEDs Look Forward to a Bright, White Future"

Awards

[1] Award for Outstanding Achievement in Polymer Science and Technology, the Society of Polymer Science, JAPAN (2023)

[2] Fujiwara Award, the Fujiwara Foundation of Science (2021)

[3] Award of the Society, the Chemical Society of JAPAN (2021)

[4] Fellow, the Society of Polymer Science, JAPAN (2018)

[5] Karl Ferdinand Braun Prize, Society for Information Display, USA (2015)

[6] Highly Cited Researcher, Thomson Reuters (2014, 2015, 2016, 2017, 2018)

[7] Medal with Purple Ribbon, Japan (2013)

[8] Science and Engineering Award, Yamagata Prefecture, Japan (2009)

[9] Fellow Award, Society for Information Display, USA (2008)

[10] Herman F. Mark Technology Medal, Polytechnic University, USA (2007)

[11] Sakurai Award, Optoelectronic Industry and Technology Development Association, JAPAN (2003)

[12] Special Recognition Award, Society for Information Display, USA (2002)

[13] Award of the Society of Polymer Science, the Society of Polymer Science, JAPAN (2002)

Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC): All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to ieee-history@ieee.org. Please see the Milestone Program Guidelines for more information.

Please email a jpeg or PDF a letter in English, or with English translation, from the site owner(s) giving permission to place IEEE milestone plaque on the property, and a letter (or forwarded email) from the appropriate Section Chair supporting the Milestone application to ieee-history@ieee.org with the subject line "Attention: Milestone Administrator." Note that there are multiple texts of the letter depending on whether an IEEE organizational unit other than the section will be paying for the plaque(s).

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