In a step toward making display screens out of a material not too different from garbage bags, researchers for the first time have got plastic transistors and glowing diodes to work together. The success, reported in tomorrow's issue of Science and in the 13 July issue of Applied Physics Letters, opens the way to lightweight, flexible displays that could someday challenge conventional televisions and laptop screens and open up entirely new uses for displays such as large-area illuminated signs that can be rolled up and carted away.
The prospect of all-organic displays has been tantalizing researchers for years. Each point of light is a single light-emitting diode (LED) powered by an electric current, which is switched on and off by a transistor. Unfortunately, most organic transistors can't muster the current that organic LEDs typically need to shine. Last year, however, saw the advent of a new breed of high-current organic semiconductors. Two teams aiming to make all-organic displays, one at Lucent Technologies' Bell Laboratories in Murray Hill, New Jersey, and one at Cambridge University, both settled on one of these new organics, a chainlike polymer known as regioregular poly(hexylthiophene).
Henning Sirringhaus of Cambridge and his colleagues describe in Science how they fashioned this polymer into an organic transistor and used it to drive a conventional polymer-based LED built directly on top. The Bell team, led by physicists Ananth Dodabalapur and Zhenan Bao, report in APL that they made a similar transistor but then crafted an organic LED along side.
The marriage of organic electronics and diodes "is a breakthrough that the field of organic displays has been looking for," says Yang Yang, an organic display expert at the University of California, Los Angeles. The advance should allow researchers to use simple, low cost fabrication methods such as screen printing and inkjet printing to lay down all the different materials needed to create displays, says Yang. "It will be very exciting to see what you can do with all-organic systems," adds James Sturm, an organic display expert at Princeton University in New Jersey.