The increasing viability of OLED as a source of light has led to an increasing number of commercial companies expressing confidence in this new solid-state lighting technology.
By Novaled AG
In addition, both on-state and off-state can be used for decorative impact. Transparent OLED panels made on glass substrates will be able to function as windows during the day and light up after dark, either mimicking natural light or providing attractive interior lighting. Furthermore, they could also function as privacy shields in homes or offices during the day (Figure 1).
OLEDs made directly on metal substrates such as steel make it possible to introduce lighting into a widely used architectural product without compromising surface integrity. In addition, such OLEDs demonstrate good heat dissipation and are therefore ideally suited for high-brightness lighting applications. The use of metal plates as substrates offers a route to fully flexible and robust products.
To date, rigid glass and metal substrates have been used to make reliable OLEDs. However, research is being carried out with plastics and thin metal substrates to make flexible OLED lighting, all of which should reach the level of industrialization in due course.
OLED devices comprise a substrate material, metallic electrodes, and functional organic materials that are designed to be environmentally safe. Furthermore, they do not contain mercury and are made on a variety of substrates that can be opaque or transparent, rigid or flexible, giving rise to different product features and performance levels.
The organic semiconductor materials are molecular, carbon-based substances that form extremely thin, amorphous layers that typically consist of separate-change-conduction layers and light-emission layers that are deposited in a predefined order and referred to as an OLED stack. Upon the application of a low voltage across the OLED, charge carriers are injected from the electrodes into the organic layers. On reaching the emission layer, which is the middle layer of the OLED, the charge carriers recombine and produce light of a predefined color.
The further development of OLED-lighting technology depends on enhancing the performance and stability of the OLED stack. Electrical improvements—reducing the driving voltage, for example—can be realized by doping techniques. Phosphorescent emitter materials are more efficient than fluorescent, and improving blue emitter lifetime is the subject of intensive research.
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