Toshiba Corp will announce the details of its transmissive OLED panel at SID Display Week 2013 (SID 2013), an academic conference on display technologies, which will run from May 20, 2013.
The panel is called "Transmissive Single-sided Light Emission OLED Panel," and its prototype was exhibited at Lighting Japan 2013, a trade show that took place from Jan 16 to 18, 2013.
One of the notable features of OLED lighting panels is that they can be transparent when they are turned off. In general, to realize a transparent OLED panel, transparent electrodes such as ITO (indium tin oxide) electrodes are used on both sides of the panel.
However, there are two problems with transparent OLED panels made in this way. First, light comes out from both sides of the panel, making some applications difficult. For example, when such a transparent OLED panel is used for a window, it provides light not only to the room but also to the outside of the room, wasting electric power and causing light pollution.
Second, when the panel is emitting light, neither side of the panel looks transparent. In other words, the panel loses its transparency at the time of emitting light. And it is not easy to control the direction of light extraction with a transparent OLED panel having a common structure.
Stripe-shaped nontransparent electrodes
Toshiba solved this problem by using its own method. It stopped using transparent electrodes such as ITO electrodes on both sides of the panel. Specifically, the company used nontransparent metal electrodes on the back side of the panel. And the metal electrodes were arranged in a thin stripe pattern.
The area having the metal electrodes is not a so-called transparent OLED panel, enabling to extract most of the light from the front side of the panel. On the other hand, in the area where there is no metal electrode, the light is bi-directionally transmitted, making the area transparent even when the panel is emitting light. As a result, the panel looks transparent when seen from the back side even at the time of emitting light.
"That's why we use the word 'transmissive' instead of 'transparent,'" Toshiba said.
The stripe-patterned metal electrodes are 140μm-wide thin electrode lines with a pitch of 500μm. They were formed with a low-temperature vapor deposition technology.
The panel and its light-emitting area measure 180mm x 90mm and 164 x 72mm, respectively. It has a thickness of 1.4mm, brightness of 450-800cd/m2, power consumption of 0.7-1.6W and color temperature of 3,300K. The brightness ratio between the front and back sides of the panel emitting light is 70:1. The light transmission rate of the panel is 68% while the electrical resistance of the electrode is very small, Toshiba said.
Lighting apparatus can be transparent even when emitting light
Toshiba plans to commercialize the transmissive OLED panel, expecting that it will be used for new applications that are different from those of common transparent OLED panels. Specifically, the company is considering using the new panel for seeing an object through the panel while illuminating the object.
Toshiba has already prototyped a "light-emitting poster" and "light-emitting glasses," whose lenses emit light. Also, the company is considering using the panel for dental treatment, aquariums, showcases, etc.