At QD Vision, older deposition techniques have led to either single-color or low-resolution displays in which each color pixel is millimeter scale, Coe-Sullivan says.
The new method also produces more energy-efficient light-emitting devices. That’s because the solvent is evaporated before the quantum dots are deposited. “Putting the material on a stamp and then transferring it dry is a great way of doing things,” says Ghassan Jabbour, a materials-engineering professor at Arizona State University. “It avoids any contact of the bottom layers”–the surface on which the dots are being deposited–“with the solvent.” That improves efficiency, Jabbour says, since “solvents can interact with the bottom organic layer and degrade the device performance.” Indeed, Bulovic says that the devices the researchers built using the stamps are the most efficient they’ve made in the lab.
Using the older deposition technique, QD Vision has already developed two commercial products–one for general illumination and one for consumer-electronics devices–that the company plans to launch by May 2009. But, Coe-Sullivan says, “to make high-information-content displays like TVs or cell phones, you need to be able to pattern at the 40- to 100-micrometer level. As we get to future product platforms that involve high-resolution multicolor displays … the stamp printing technique will be the enabler.”
Coe-Sullivan says that QD Vision should be able to use quantum-dot stamps to make displays as big as current LCDs, which could give quantum dots an advantage over OLEDs. Large OLED displays are difficult to make, because their manufacture involves spraying organic-semiconductor molecules through a stencil that has nanoscale pinholes in it. Although Samsung has demonstrated prototypes of 40-inch OLED TVs, the only commercially available model is Sony’s 11-inch TV, which sells for $2,500. Coe-Sullivan expects quantum-dot displays to be more cost-competitive with LCD TVs.
It might even be possible, Jabbour says, to use the new deposition technique for roll-to-roll printing, which would enable quick production of flexible displays. “A roll-to-roll printer is nothing but a stamp that is rolling around at 100 kilometers per hour,” Jabbour says, “so it doesn’t really matter if it is a flat or a round stamp.”
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