Exploring a New Generation of Signage and Graphics Materials
"In the case of small-molecule or crystalline OLED materials, they're usually deposited using conventional vacuum thermal evaporation," Mahon says. "They're put in a crucible or boat. That boat is heated up, and those materials then evaporate or sublime. They then recondense on a substrate that is positioned upside down in side the vacuum chamber."
OLED displays are either passive matrix or active matrix. A passive-matrix display emits lights by conducting energy through columns and rows of anodes and cathodes. Thin films of organic materials are sandwiched between the anodes and cathodes. Application of electrical current causes the pixels in the two-dimensional array to emit light. Pixels become brighter as more current is applied. MP3 players, cell phones, and other portable electronics are popular candidates for passive-matrix OLEDs.
Active-matrix OLEDs use thin-film transistors to continuously control the flow of current through each pixel in a display. The active-matrix OLED is designed to use less power than passive displays, which makes the technology a better choice for portable devices in which battery power must be conserved. Active-matrix OLEDs also have been used in the production of prototype televisions and other types of larger displays.
White, phosphorescent, transparent/top-emitting, and flexible OLEDs are other technologies UCD develops. White OLEDs have the potential to produce 200 lumens/W, which Mahon says exceeds what conventional fluorescent tubes can provide. These OLEDs can be used in displays and have potential uses in illuminating frontlit and backlit graphics. This technology also is of interest to the US Department of Energy's solid-state lighting initiative.
Phosphorescent OLEDs, she explains, use metallo-organic molecules and offer a great deal of power efficiency. For instance, a display that would normally consume 1 watt of power could consume just watt. "It also has a dramatic impact as you get to larger and larger displays, where heat dissipation becomes more of an issue," she says.
Transparent and top-emitting OLEDs share a similar method of construction. Transparent OLEDs emit light from the top and bottom. The use of a transparent anode, cathode, and substrate makes that possible. The use of an opaque substrate makes what would be a transparent OLED a top-emitting display instead.
"The concept of having a transparent display is one of those wild kinds of technologies," Mahon says. "The thought of being able to have displays integrated directly into a windshield or window for signage and advertising is tremendous."
The materials that drive the displays described here have yet to become completely accessible to graphics and industrial printers. But as the development of these technologies continues, printing companies will likely be among those who reap rewards from the ability to produce portable and addressable signage, promotional displays, and much more. In the mean time, we can look to the systems described here as bold and revolutionary signs of things to come.
Did you enjoy this article? Click here to subscribe to the magazine.