Rinzler’s new electronic devices, described online in the journal Nano Letters, also operate at a tenth of the voltage of conventional OLED electronics, which saves power. The Florida researchers have not yet made large-area OLED displays driven by the vertical transistor arrays, but Rinzler says the transistors operate at suitable current and voltage to do so. While the researchers have so far been making these arrays on glass, the techniques used to make them are compatible with flexible substrates and could be used to make flexible OLED displays.
The vertical electronic structure was first proposed in 1994 by Yang Yang, professor of materials science and engineering at the University of California, Los Angeles, and Alan Heeger, professor of materials science and engineering at the University of California, Santa Barbara. Heeger shared the 2000 Nobel Prize in Chemistry for the discovery and development of conductive polymers like the ones used in the new device. In the mid-1990s, Yang and Heeger began developing these devices through a company called UNIAX that was subsequently acquired by DuPont. When the two did their original work, the performance of the available materials wasn’t as good as it is today.
“Carbon nanotubes weren’t available in 1994,” says Yang. In Rinzler’s device, he says, the thin nanotube layer allows very little current leakage, a problem that drained power from previous designs. The Florida devices also switch much faster than was possible in the past. “They did an excellent job of making the device work much better. I’m sure this paper will have an important impact on organic electronics,” he says.
Rinzler is now working to simplify the OLED display architecture in hopes of further reducing manufacturing costs and complexity. Instead of building a light-emitting pixel next to transistors, Rinzler wants to build low-power organic transistors that emit light themselves. His group has demonstrated that it’s possible to make light-emitting organic transistors if the active materials are electroluminescent, but these transistors only operate at high voltages, making them impractical. Rinzler believes that the vertical, nanotube-electrode-based architecture could greatly improve the efficiency of these devices.