Nanoscale SiLEDs Emit Multiple Colors

Highly efficient LEDs composed of silicon nanocrystals but without heavy metals can now emit light in a variety of colors.

Silicon dominates in the microelectronics and photovoltaics industries but has long been considered unsuitable for LEDs. For nanoscopic dimensions, however, this argument proves invalid. Minute silicon nanocrystals, which consist of only a few hundred to a thousand atoms, can produce light and hold potential as highly efficient light emitters.

In a joint project, scientists from Karlsruhe Institute of Technology (KIT) and the University of Toronto in Canada have developed nanoscale silicon-based LEDs (SiLEDS) free of heavy metals such as cadmium selenide, cadmium sulfide and lead sulfide, which are toxic and costly.

Liquid-processed SiLEDs developed by scientists from KIT and the University of Toronto. By changing the size of the silicon nanocrystals, the color of light emitted can be varied. Courtesy of F. Maier-Flaig, KIT/LTI.

Previous manufactured SiLEDs were limited to the red visible spectral range and the near-infrared, but the new diodes can emit multiple colors.

“Controlled manufacture of diodes emitting multicolor light, however, is an absolute novelty," said Florian Maier-Flaig, a scientist at KIT’s Light Technology Institute and a doctoral student at the university’s School of Optics and Photonics.

The investigators were able to adjust the color of the light emitted by the LEDs by separating nanoparticles according to their size.

“Our light-emitting diodes have a surprising long-term stability that has not been reached before,” Maier-Flaig said.

The increased service life of the components in operation is a result of using nanoparticles of one size only, enhancing the stability of the sensitive thin-film components. Short circuits from oversized particles were excluded.

The development is also characterized by homogeneity of the luminous areas.

“With the liquid-processed silicon LEDs that may potentially be produced on large areas as well as at low costs, the nanoparticle community enters new territory, the associated potentials of which can hardly be estimated today,” said Geoffrey A. Ozin, a distinguished research fellow working at KIT’s Center for Functional Nanostructures. “But presumably, textbooks about semiconductor components have to be rewritten.”

The scientists are now working to further develop the SiLEDs in cooperation with other partners.

Findings were reported in Nano Letters (doi: 10.1021/nl3038689).

For more information, visit: www.kit.edu