Another advantage of amorphous silicon over organic materials is that its electronic performance is well known. “Organics are less well developed,” says John Rogers, professor of materials science at the University of Illinois, Urbana-Champaign. “[Organic components] have uncertain stability and limited long-term reliability; they also have not been used in large-scale applications.”
The transition from thin-film solar to printing display transistors was relatively simple, says PowerFilm’s Jeffrey. The major difference is that the layers are deposited in a different order. Some layers also need to be doped–adding impurities to change a layer’s electrical properties–in a different way. “We used our solar-cell machines to do the first development work,” he says. “It was very straightforward.”
Phicot is planning to move to a facility in Silicon Valley by the end of the year to take HP’s SAIL technology to a large space.
But the process is far from perfect. Jeffrey says that the engineers are quickly solving many of the defect challenges–the major obstacle to mass production at this point. For instance, the process must be fine-tuned so that the plastic isn’t stressed in a way that could, down the line, result in defective circuitry.
Another challenge is making sure that the plastic is as defect-free as possible to start with. “Your plastic has to be smooth,” says Alberto Salleo, professor of materials science and engineering at Stanford. “And as it goes through the rolls it shouldn’t expand or crack.”
Jeffrey says there may be ways to adapt the electronics to flaws in the plastic. “We have a possible option of designing our circuitry to tolerate those” he says.