Based on organic light-emitting diode (OLED) technology and implemented by means of a printing machine, patterned and flexible light-emitting surfaces have been created on advertising displays, information signs and lighting fixtures by VTT Technical Research Center of Finland Ltd. The method also enables transparent smart surfaces to be attached to window panels or packaging, VTT recently explained in a technology paper.
OLED is commonly used in mobile phone displays and television sets. Until now, though, it has only been found on glass surfaces and implemented using traditional microelectronics manufacturing methods.
Using VTT's method, OLED elements can now be printed not only onto glass or steel surfaces but also onto flexible plastic films, enabling significantly larger light surfaces and expanding the possibilities of the technology.
Traditional printing methods, such as gravure and screen printing, that enable very large production volumes are used for manufacturing OLED light surfaces. Production is, therefore, possible in facilities such as traditional printing houses, said VTT.
Manufactured in this manner, OLED light surfaces measure around 0.2 mm thick, and include electrodes and polymer layers measuring up to a few hundred nanometers, in which light emission occurs. This phenomenon is called electroluminescence; it entails an organic semiconductor emitting light in an electric field. The luminosity of OLED (lm/W) amounts up to around one-third of an LED's luminosity. It has one advantage: OLED emits light throughout its entire surface, whereas LED is a spotlight technology, explained VTT in its recently released technology paper.
At this point, VTT's plastic OLED film will only emit light for around a year, since light-emitting polymer materials are susceptible to oxygen and moisture, said VTT. In the future, the film's lifespan will increase as the development of screen protectors continues and the film's application possibilities grow.
"The plastic film is optimally suited to advertising campaigns, in which large light-emitting surfaces can be used to draw significantly more attention than can be gained through mere printed graphics or e-ink-type black-and-white displays that do not emit light," stated VTT Head of Research Area Raimo Korhonen.
It is also possible to use OLED light as a transmitter in wireless data transfer, which opens up new possibilities for using printed light surfaces in Internet of things applications, said VTT.