By changing the size of the silicon nanocrystals, the colour of the light emitted by the liquid-processed SiLEDs can be varied

Silicon LEDs free from toxic heavy metals created

Silicon-based LEDs that are highly efficient, low-cost and free from toxic heavy metals have been developed by researchers.

A team of chemists, materials researchers, nanoscientists and opto-electronic experts from the Karlsruhe Institute of Technology (KIT) in Germany and the University of Toronto in Canada have succeeded in manufacturing silicon-based light-emitting diodes (SiLEDs), which can emit light in various colours.

In contrast to cadmium selenide, cadmium sulfide or lead sulfide used by other groups of researchers, the silicon used by this group for the light-emitting nanoparticles is not toxic, is highly abundant and is available at low cost.

Silicon dominates in microelectronics and photovoltaics industry, but was considered unsuitable for light-emitting diodes for a long time, but now the research team have shown this is not true for nanoscopic dimensions. Minute silicon nanocrystals of a few hundred to a thousand atoms have considerable potential as highly efficient light emitters.

So far, manufacture of SiLEDs has been limited to the red visible spectral range and the near infrared.

“Controlled manufacture of diodes emitting multicolour light, however, is an absolutely novelty,” said Florian Maier-Flaig, from the Light Technology Institute of KIT and doctoral student of the Karlsruhe School of Optics and Photonics.

“Moreover, our light-emitting diodes have a surprising long-term stability that has not been reached before.”

KIT scientists specifically adjust the colour of the light emitted by the diodes by separating nanoparticles depending on their size and they have achieved a high homogeneity of the luminous areas.

The increased service life of the components in operation is due to the use of nanoparticles of one size only, which enhances the stability of the sensitive thin-film components and also means short circuits due to oversized particles are excluded.

Geoffrey Ozin, who is presently working as a KIT distinguished research fellow at KIT’s Centre for Functional Nanostructures, said: “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. But presumably, textbooks about semiconductor components have to be rewritten.”

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