Polymer LED emits in near-infared

17 Jun 2002

In today's Science, researchers reveal a polymer-based LED aimed at fiber-to-the-home applications.

From Opto & Laser Europe magazine

Researchers in Israel have successfully combined III-V semiconductors with conjugated polymers to give an efficient organic light-emitting diode (OLED) that emits in the near-infrared (Science 295 1507).

Until now, many researchers had believed that it was impossible to obtain efficient near-infrared emission from polymers due to the polymer's inherent molecular vibrations that deactivate any source of near-infrared radiation.

To make the device, Nir Tessler and colleagues at the Israel Institute of Technology in Haifa and the Hebrew University in Jerusalem used near-infrared-emitting nanocrystals consisting of a GaAs core and a ZnSe shell. Once an organic ligand is added to the outer shell, the nanocrystals are soluble and can be blended with the polymer solution. Devices can then be made using ink-jet printing technology.

Tessler told Optics.org: "I have always thought that the presence of the shell may help us to suppress the so-called inherent deactivation. And after two years of joint research we have been proven right."

He says that the device, which emits at 1.3 µm and has an external efficiency of 0.5%, is ideal for fiber-to-the-home applications.

"Components for fiber-to-the-home need to be cheap and there will need to be lots of them," said Tessler. "The players at the telecoms market seem to believe that current technology platforms such as indium phosphide or gallium arsenide will not meet the price criteria."

He believes that polymer-based devices can meet this need for low-cost components because of their easy manufacturability. But he admits that there are performance issues.

"Our device structure is far from optimal. For example, its turn-on voltage of 15 V is rather high. It is also a single-layer device and we have preliminary results using double layer devices showing a significant improvement. We are also extending the wavelength up to 1500 nm so that we can cover the other telecoms band as well."

Tessler also believes he can use this material system to make the first electrically-pumped polymer laser.

Author
Nadya Anscombe is editor of Optics.org and Opto & Laser Europe magazine.