"SPring-8" analysis material for OLED lighting manufacturing analysis

The manufacturing method of the organic EL illumination has two options of an evaporation method and a coating method. Further, even if it is the same coating method, there are methods using materials and element structures similar to the vapor deposition method, and methods using materials and structures peculiar to the coating method. KONICA MINOLTA ADVANCED LAYERS uses the former, while Sumitomo Chemical uses the latter.

KONICA MINOLTA ADVANCED LAYERS said that tremendous progress has been made in the last year. "The film-forming yield of the low-emitting layer and the like has been greatly improved, and the quality of the film is similar to that of the vapor deposition method" (the company's OLED business promotion center, Nakamura Takahiro). The detailed structure of the luminescent material was analyzed by using the large-scale radiation light facility "SPring-8" in Hyogo Prefecture, and the cause of the problem such as solidification was found, and the direction of improvement was found.

In order to make a luminescent material have a variety of functions, Sumitomo Chemical has designed a polymer material and promoted it in the direction of simplifying the structure of components.

Uncommon competitive weapon

There are also manufacturers that have developed an organic EL lighting element structure that emphasizes color and looks like a display. For example, Mitsubishi Chemical and Pioneer. As with the display, full color can be achieved with one panel by applying red (R), green (G), and blue (B) materials to the luminescent layer. KANEKA and Sumitomo Chemical, which also pay attention to pleochroism, are very different from the policy of changing colors according to panels.

The difference from the display is that the RGB sub-pixels are not mosaic, but strips. A base layer such as Mitsubishi Chemical and the light-emitting layer can be formed by a low molecular material coating method, and it is planned to mass-produce panels using a small-scale device of the first generation (G1) scale by the end of 2013.

Showa Denko has adopted a component construction that is not similar to any other. That is, "COLED (cavity organic light emitting diodes)" developed in cooperation with SRI International of the United States, that is, a method of forming a film on the surface of a glass substrate and forming a film thereon. However, Showa Denko has not announced the specific effects, except for setting a very high target of “2015 luminous efficiency of 150 lm/W”. The company's published organic EL components have a luminous efficiency of only 30 lm/W. Even so, the company is confident that "COLED is a powerful weapon to compete in the development of other companies that are easy to distinguish. It is not surprising to hear other companies reach 128lm/W" (Showa Suzuki Hiroyuki, Chief of the Strategic Marketing Center of the Technical Research Office of the Electrician Research and Development Department.

A new generation of transparent electrodes unveiled

Progress has also been made in the development of transparent electrodes that have greatly improved luminous efficiency. KONICA MINOLTA ADVANCED LAYERS has developed an excellent transparent electrode with a sheet resistance of 1 Ω/□ and a light transmittance of 84% including a substrate by combining silver (Ag) nanowires and a transparent conductive resin (Fig. 10). ). Moreover, it can be produced by a coating method, and the substrate is flexible.

Figure 10: Is the new generation of transparent electrodes implemented in a “combination”?

KONICA MINOLTA ADVANCED LAYERS combines Ag nanowires with conductive organic materials to develop a transparent conductive film (a) with low sheet resistance and high light transmittance required for large organic EL panel transparent electrodes. Toshiba also combined Ag nanowires and graphene to develop a low-thin film resistance transparent conductive film (b). The light transmittance is slightly lower. ((b) Picture Photography: Toshiba)

The resistance of the transparent electrode accounts for a large proportion in the organic EL illumination panel, and the larger the panel size, the higher the ratio. Therefore, in order to enlarge the panel size without lowering the luminous efficiency, the resistance of the transparent conductive film must be small. KONICA MINOLTA ADVANCED LAYERS said, "ITO has a problem of excessive resistance before discussing whether it is flexible. It must be reduced to 1 Ω/□ or less."

In September 2012, Toshiba also combined Ag nanowires with carbon material graphene to develop transparent electrodes with low sheet resistance values. In the future, we will promote the development of these new generations of transparent electrodes and contribute to the increase in the size of organic EL lighting panels.