Sunday, November 20, 2011

Nanocrystals cheaper to catch Solar Power

Technion researchers polarize a nanometric-sized crystal by changing the composition of surrounding molecules. In the future, this could improve efficiency of 3G solar photovoltaic cells.

Technion researchers from the Sara and Moshe Zisapel Nano-Electronics Center successfully polarized a nanocrystal by changing the composition of the molecules surrounding it. This finding was just published in the prestigious scientific journal, Nature Materials.

Doctoral student, Nir Yaacobi-Gross, under the supervision of the head of the Zisapel Center, Prof. Nir Tessler, exchanged some of the molecules attached to the surface of the nanometric-sized crystal with different molecules whose chemical or atomic group anchoring them to the crystal’s surface was different. The researchers discovered that the lack of uniformity in the molecular covering caused the crystal to partially polarize. The research group led by Prof. Asher Schmidt of the Schulich Faculty of Chemistry also contributed to understanding the molecule-crystal connection process.

As the paper shows, this discovery will likely have far-reaching consequences in as far as significantly improving the efficiency of solar cells. These are 3G photovoltaic cells that are being intensively developed around the world due to their relatively low cost (and therefore, their suitability for mass production). The solar cells used today are mostly silicon based and are expensive both in terms of production costs and in the energy required to manufacture them. The discovery by the Technion researchers changes the ability of nanocrystals to receive or give electrons to material surrounding it, which essentially means that they have changed the crystal’s characteristics.

“Nano crystals of different materials are used to develop new light sources and solar cells.”

“Nano crystals of different materials are used to develop new light sources and solar cells,” explains Prof. Tessler. “The nanocrystal is produced in a solution, is about 2-8 nanometers in diameter and covered by an organic molecule that stabilizes it and allows the nanocrystal to be dissolved in the proper fluids. In this case the solution is actually an ink containing opto-electronic materials and hence today there is a lot of activity going on around the world designed to integrate these materials in the field of printed electronics that will produce sheets of lights or sheets of solar cells.”

The researchers emphasize that in order to enable the integration of these new materials in opto-electronic devices, it is important to achieve control over their characteristics so as to be able to relate to them as building blocks to be used in engineering an advanced device.

In the early stages of the research in the Zisapel Center, it was found that organic molecules could be used to move the relative location of the particle’s level of energy. What surprised the researchers at this stage was the fact that the most important factor in this move was the atom found at the end of the molecule, which connects to the nanocrystal. The researchers showed that not only can the energy levels of the nanocrystal be moved relative to materials or to other nanocrystals, but that it was possible to change areas of this tiny crystal (approximately 4 nanometers in size) relative to other areas. “This study showed that we had a crystal that is inorganic but surrounded by organic molecules such that it constitutes an entity that is a hybrid of organic and inorganic material,” stresses Prof. Tessler. This distinction requires a change in the theoretical approaches that analyze these crystals and ignore their organic part (the organic molecules attached to them), mostly because “it just contributes to creating a solution.”

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