Professor Kido is an expert in the field of the chemistry of functional organic materials and organic light-emitting diodes (OLEDs). He started working on the development of OLED materials and devices in 1989 soon after he joined Yamagata University as an assistant professor. Besides developments of OLED materials, he succeeded, for the first time, to develop white-light-emitting OLEDs in 1994. His other inventions regarding device structures, including tandem OLEDs, have been used in commercialized OLED displays. His main achievements are introduced below.

1. Electroluminescence from lanthanide complexes
Prof. Kido is the first to report on the electroluminescence of lanthanide complex observing green electroluminescence from terbium complex in 1990. He also succeeded to fabricate Eu complex-based red-light emitting OLEDs in 1991. Because electroluminescence from these lanthanide complexes is from the multiplet excited states, the possibility of 100% internal quantum efficiency was indicated for the first time. Later, he demonstrated an internal quantum efficiency of 100% (30% external quantum efficiency) by using phosphorescent Iridium complex, which is the world-record high efficiency at that time.

2. Development of high performance organic semiconductor materials
To improve the performances of OLEDs, one of the most promising approaches is to use semiconductor materials with high carrier mobility. For example, Prof. Kido developed a series of materials, which exhibits both intramolecular and intermolecular H-bonding abilities, to attain the high order of horizontal molecular orientation in n-Type, electron-transporting materials (ETMs). Among such semiconductor materials, pyridine-containing materials exhibit high electron-transporting capabilities due to the molecular orientation through the inter-molecular hydrogen-bonding. In particular, the peripheral pyridine rings provide weak intermolecular hydrogen-bonding ability to complementally support a pai?pai stacking. This type of materials is now widely used in high-performance OLEDs. In addition to the n-type, a variety of p-type semiconductor materials has also been developed. He reported hexaphenylbenzene-based sterically bulky hole-transport materials with deep ionization potential and high triplet energy. By using these materials, he realized high external quantum efficiency and long operation lifetime. Prof. Kido has kept his interest in the small molecular weight materials and developed new materials. 　

3. Development of high efficiency OLEDs
With regard to the high efficiency OLEDs, Prof. Kido proposed the means to reduce the drive voltage by using chemically doped interface layers. In these devices, organic layers contacting the electrode is chemically doped and the gap states are formed so that carriers are injected from the electrode to the organic layer through the gap states. Having such doped layers, the contact between organic layer and the electrode becomes ohmic and the drive voltage of the device becomes lower than those of the conventional devices, resulting in higher luminous efficiency. In addition, using the doped layers, fabrication of thick conducting layers, composed of the doped materials, becomes possible so that the optical length of the organic layers can be easily controlled to optimize light-out coupling efficiency. Such chemically doped layers have been used in the commercialized OLED displays.

4. White light-emitting OLEDs
Prof. Kido's work is not limited to the development of organic materials. He has been working on device physics and designing new device structures for high performance and color tuning. He is actually 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 resulting emission becomes white. He has been continuously working on the development of white OLEDs, and also started a company Lumiotec Inc. as a co-founder to manufacture white OLED panels for general lighting.

5. Long-life tandem OLEDs
Prof. Kido 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. The key technologies of this type of device is to use charge-generation layers between emissive layers. The combination of electron-donor materials and electron-accepting materials is a simple and effective way to connect emissive units. White OLEDs, having tandem structures, have been used for white OLED panels for general lighting. Today, it has also become an essential technology for large-size OLED displays combined with RGB color filters.

6. Solution-processed OLEDs
Among the Prof. Kido' s work on solution-processed OLEDs, the polymer-based OLEDs based on poly(vinylcarbazole), PVK, published in 1993 was the first bright blue emitting polymer device developed. He has continued to work on PVK and, by molecularly doping PVK with organic fluorescent dyes, he succeeded to realize emission of three primary colors of red, green and blue. Prof. Kido also synthesized new polymers for OLED that include pendant-type polymers and main chain-type polymers. Towards low cost production, he has kept working on solution-processed OLEDs, and succeeded the fabrication of tandem OLEDs. More than ten thin layers are stacked by spin coating, using orthogonal solvents. Not only with polymers, but he demonstrated efficient solution-processed multilayer OLEDs with small molecules. On the basis of estimates from a solvent resistance test of small molecules, he demonstrated that materials with molecular weight of 800-1000 can afford conventional small host molecules sufficient resistance to alcohols used for processing upper layers. This allows us to construct multilayer OLEDs through subsequent solution-processing steps, achieving record-high power ef?ciencies for solution-processed OLEDs

Thus, Professor Kido's great contributions deserves well to the Chemical Society of Japan (CSJ) Award.