Solar energy efficiency could double using quantum dots

Could quantum dots double efficiency?

As previously reported, the arms race for energy conversion from light to electricity could legitimise alternative energy and speed its rise in European and global infrastructure. As such, several research facilities across the world are experimenting with varying surface structures in an effort to increase the efficiency of solar cells.

Using the current method of silicon, the capacity to take sunlight and turn it into electricity through photovoltaic cells is hopelessly woeful, around 20 percent, although Drs Andreas Bett and Frank Dimroth from ISE, were able to record over 40 percent energy efficiency by using a metamorphic triple junction cell, although this is still some time off going into production.

Now a team of scientists from the university of Minnesota and Texas claim they can convert 66 percent of available sunlight using nanoscale crystals called quantum dots.

Solar cells routinely lose heat from the high end of the spectrum, which results in high-energy sunlight being too hot to be converted into electricity. The research team led by chemist Xiaoyang Zhu has found that by using quantum dots, the hot electrons are conducted and not lost. This is due to the speed of the high-heat transfer, that takes place in less than 50 femtoseconds (to put that in some kind of scale, a femtosecond is one quadrillionth of a second, or virtually instantaneous) and at that speed, fewer of the jiggling and excited electrons are lost to heat, making a 66 percent energy transfer possible.

However, like most promising alternative methods, there is a drawback; namely that conventional quantum dots are made of heavy toxic metals, which would be unworkable and unrealistic on a large scale. However, according to Zhu, in this process, quantum dots could be used with other materials, opening up the potential to build a high efficiency solar cell with quantum dots made of non-toxic materials.

It isn't the first time that scientists have potentially broken the 50 percent efficiency mark. Using a similar nanotechnology, a team of researchers in Idaho claim they can obtain an impressive 80 percent efficiency by using a solar surface panel that is printed with minuscule nano-antennae that capture infra-red radiation; again, working to utilise all of the sun's heat and light, not just a fraction of the spectrum.

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