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February 11, 2010

IBM Makes Efficient Solar Cells From Cheap Materials and UK Researchers Make Hydrogen from Sunlight with 60% Efficiency

1. Researchers at IBM have increased the efficiency of a novel type of solar cell made largely from cheap and abundant materials by over 40 percent. According to an article published this week in the journal Advanced Materials, the new efficiency is 9.6 percent, up from the previous record of 6.7 percent for this type of solar cell, and near the level needed for commercial solar panels. The IBM solar cells also have the advantage of being made with an inexpensive ink-based process.

The new solar cells convert light into electricity using a semiconductor material made of copper, zinc, tin, and sulfur--all abundant elements--as well as the relatively rare element selenium (CZTS). Reaching near-commercial efficiency levels is a "breakthrough for this technology".



The IBM researchers are also investigating ways to improve the efficiency of the new solar cells, with the goal of reaching about 12 percent in the laboratory--high enough to give manufacturers confidence that they could be mass produced and still have efficiency levels of around 10 percent, says David Mitzi, at IBM Research, who led the work. Beard recommends targeting 15 percent efficiency in the lab, and Mitzi says this should be possible by improving other parts of the solar cell besides the main CZTS material, or by doping the semiconductor with other trace elements (which is easy with the ink-based process).

What's more, commercial cells will likely use different materials for conducting electrons. The experimental cells used indium tin oxide, which is limited by the availability of indium. But Mitzi says several other conductors could work as well.

One key next step is to completely replace the selenium in the solar cells with sulfur. For the record-efficiency cell, the researchers replaced half of the selenium used in a previous experimental cell. If all of the selenium could be replaced, the cells could, in theory, supply all of the electricity needs of the world. (Provided there are suitable means for storing and redistributing power for use at night or on cloudy days.)

2. Sunlight + water = hydrogen gas, in a new technique that can convert 60 per cent of sunlight energy absorbed by an electrode into the inflammable fuel.

Thomas Nann and colleagues at the University of East Anglia in Norwich, UK, dip a gold electrode with a special coating into water and expose it to light. clusters of indium phosphide 5 nanometres wide on its surface absorb incoming photons and pass electrons bearing their energy on to clusters of a sulphurous iron compound.

This material combines those electrons with protons from the water to form gaseous hydrogen. A second electrode – plain platinum this time – is needed to complete the circuit electrochemically.

The inorganic materials used in the University of East Anglia's system are more resilient. Their first generation proof of concept is "a major breakthrough" in the field, they say, thanks to its efficiency of over 60 per cent and ability to survive sunlight for two weeks without any degradation of performance.

Each cluster is 400 times better at netting photons than organic molecules used in previous systems





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