Better cells

By Archita Bhatta
Last Updated: Saturday 04 July 2015

Using mercury nanotubes

india may be able to produce solar cells with a greater capacity to absorb solar energy. The secret behind this extra capacity lies in mercury compound nanotubes, scientists at iit Delhi have found out. Nanotubes, because of their structure, exhibit electrical and optical properties, which help in the absorption of solar energy and its conversion to electrical energy. Researchers have long dabbled with nanotube research to find an effective absorption material.

"Mercury nanotubes can absorb around 95 per cent of the solar spectrum and could act as effective absorption material," said A Ranga Rao, the lead researcher. Currently, absorption materials in solar cells are made of silicon and nanostructures of cadmium telluride, which absorbs 60-70 per cent of the solar spectrum. The problem, however, lay in manufacturing the mercury nanotubes. "There have been very few reports on the synthesis of nanostructures of mercury related compounds owing to the difficulties in handling the materials during synthesis," said the paper published in the April 15 issue of Advanced Materials.

To solve the problem of handling toxic mercury, the researchers used non-toxic mercury compounds to synthesize mercury sellenide and mercury telluride nanotubes. Then, the researchers faced another problem. Most methods of nanotube production such as high temperature evaporation took place under high temperature and high-pressure deposition conditions and were not economically viable.

The most viable one, spraying nanoparticles under an electric field, led to creation of nanocrystalline films having isolated nanoparticles. Nanotube formation required self-assembly of these particles in the presence of a molten droplet of a suitable catalyst. The researchers zeroed in on mercuric iodide as the catalyst because of its low melting point.

"This will be one of the least costly methods of synthesizing nanotubes. While 75 per cent of the mercury used is converted to nanotubes, in case of carbon, around 15 to 30 per cent is converted to nanotubes depending on the method used," said Rao. But the researchers are yet to find out the efficiency with which mercury compound nanotubes convert solar energy to electrical energy. Nanomaterials have been criticized of being less efficient than conventionally used materials like silicon. Viresh Dutta, co-author of the paper, says that even though nanomaterials have lower efficiency--10 per cent as against 14 per cent shown by silicon--the lower cost makes up for this.

The authors say their research is promising and acknowledge that a lot remains to be done to convert it into applications like infrared sensors, optical fibres or for solar cell absorption.

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