UNDERSTANDING A PRINTED TEXT. Spraying light – the fabrication of light-emitting 3D-objects

Spraying light – the fabrication of light-emitting 3D-objects

OLED (organic light-emitting diodes) technology is based on the phenomenon that certain organic materials emit light when fed by an electric current. What makes OLEDs so attractive is that they do not require a backlight to function and therefore require less power to operate; also, since they are thinner than comparable LEDs, they can be printed onto almost any substrate. The current commercial fabrication of OLEDs is a clean room technology that depends on time- and cost-driving process steps under high vacuum and/or inert atmosphere. This has limited OLED displays to smaller electronic devices such as phones, cameras and small TV screens.

"The light-emitting electrochemical cell (LEC) shares several external attributes with the OLED, but its unique electrochemical operation eliminates the principal requirement on inert-atmosphere/vacuum processing as it can comprise solely air-stabile materials," says Ludvig Edman, a professor from Sweden. "This important intrinsic advantage has inspired recent work on an ambient-air fabrication of LEC devices using scalable means; but as-of-yet, a fault-tolerant and cost-effective fabrication of large-area and uniformly-emitting devices is lacking."

Back in 2010, the group of Swedish researchers introduced a unifying model for the operation of light-emitting electrochemical cells. Now they have developed a spray-sintering method for the fabrication of LECs. Spray-sintering is a new process of depositing material that works uniquely for LEC-fabrication. The common knowledge for fabrication of light-emitting devices has been that you need to deposit a wet, homogenous film of material in order to get a smooth surface without any pinholes in it that would create black spots or uneven emission. By contrast, the properties of the LEC allow for spraying layers that are inhomogeneous and that allows for spraying of individual droplets that dry one at a time.

Through sequential spraying of three thin layers of different inks onto the substrate-of-choice, it became possible to realize uniform large-area light-emission at a low drive voltage of 3–5 V, and the researchers are working toward the realization of any desired color. The entire fabrication process can be executed under ambient air using a simple airbrush.

The research team also demonstrates that the inclusion of an additional sprayed layer allows for the creation of multi-colored light-emission patterns, and that light-emitting devices can be fabricated directly onto arbitrarily shaped surfaces. The researchers explain that the motivation behind the work has been the potential to increase the size of the objects they work with. To develop the technology further, the technology will be used for marketing items, decorations or design applications where the unique form factors of the LEC are important. When spraying 3D-objects will become commercially viable, there will be both decorative and illumination applications. A 3D-object can utilize already existing surfaces, for instance a door knob, for a child's night light, without the need to have additional light fixtures.

(http://www.nanowerk.com/spotlight/spotid=35828.php)