Can Quantum Dots Revolutionize Solar Power?


Single Layer Solar CellsThe sun will hopefully be the energy source of the future, but currently, solar power provides less than 1% of global energy. The reason isn’t due to a conspiracy among fossil fuel companies, as some media outlets apparently believe, but because of multiple inherent problems with solar technology. In a nutshell, there is a tradeoff between efficiency and cost.

For example, the current world-record for efficiency (i.e., the ability to convert light into electricity) is 44.7%, held by a multi-junction solar cell used in concentrated photovoltaics. However, for various reasons, such systems are still expensive. Cheaper solar cells, such as the ones you can mount on your roof, are more reasonably priced but have efficiences only around 10 to 20%. Thus, the “holy grail” is to design a solar cell with high efficiency and low cost.

One possible avenue is a design referred to as a dye-sensitized solar cell (DSSC). (Here is a video explaining how DSSCs work.) In a DSSC, dye molecules attached to titanium dioxide absorb photons and release electrons, creating an electric current.

Now, researchers from South Korea have added mobile quantum QTM -0.64% dots to the mix. Quantum dots (QDs) are nanoparticles that have a unique feature: They are able to generate more than one electron for every photon that is absorbed, a phenomenon known as “multiple exciton generation.” QD-DSSCs, therefore, have a higher efficiency than regular DSSCs. (See figure.)

As shown above, DSSCs containing red quantum dots (R-QD) were the best at increasing both light absorption and external quantum efficiency (a measure of how many electrons are generated per photon absorbed).

The authors told RealClearScience in an e-mail that the maximum efficiency of their system is 8.83%, which is obviously lower than most existing solar cell technologies. However, DSSCs are relatively cheap to produce, and with further research, they believe that they can crank up the efficiency way past 33.7% (the Shockley-Queisser limit, which is a theoretical limit on the efficiency of single junction solar cells).

Techies and investors should keep an eye on this emerging technology.

This article originally appeared on RealClearScience.

Source: Gede Widia Pratama Adhyaksa, Ga In Lee, Se-Woong Baek, Jung-Yong Lee & Jeung Ku Kang. “Broadband energy transfer to sensitizing dyes by mobile quantum dot mediators in solar cells.” Scientific Reports 3, Article number: 2711. Published 19-September-2013. doi:10.1038/srep02711

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New Nanomaterial Increases Yield of Solar Cells


 

New nanomaterial increases yield of solar cells  6 hours ago

Linked quantum dots – In the new nanomaterial two or more electrons jump across the band gap as a consequence of just a single light particle (arrow with waves) being absorbed. Using special molecules the researchers have strongly linked the …more

Researchers from the FOM Foundation, Delft University of Technology, Toyota Motor Europe and the University of California have developed a nanostructure with which they can make solar cells highly efficient. The researchers published their findings on 23 August 2Researchers from the FOM Foundation, Delft University of Technology, Toyota Motor Europe and the University of California have developed a nanostructure with which they can make solar cells highly efficient. The researchers published their findings on 23 August 2013 in the online edition of Nature Communications.

Smart nanostructures can increase the yield of . An international team of researchers including physicists from the FOM Foundation, Delft University of Technology and Toyota, have now optimised the so that the solar cell provides more electricity and loses less energy in the form of heat.

Solar cells

A conventional solar cell contains a layer of silicon. When sunlight falls on this layer, in the silicon absorb the energy of the (photons). Using this energy the electrons jump across a ‘‘, as a result of which they can freely move and electricity flows.

The yield of a solar cell is optimised if the is equal to the band gap of silicon. Sunlight, however, contains many photons with energies greater than the band gap. The excess energy is lost as heat, which limits the yield of a conventional solar cell.

Nanospheres

Several years ago the researchers from Delft University of Technology, as well as other physicists, demonstrated that the excess energy could still be put to good use. In small spheres of a the enables extra electrons to jump across the band gap. These nanospheres, the so-called , have a diameter of just one ten thousandth of a .

If a light particle enables an electron in a quantum dot to cross the band gap, the electron moves around in the dot. That ensures that the electron collides with other electrons that subsequently jump across the band gap as well. As a result of this process a single photon can mobilize several electrons thereby multiplying the amount of current produced.

Contact between quantum dots

However, up until now the problem was that the electrons remained trapped in their quantum dots and so could not contribute to the current in the solar cell. That was due to the large molecules that stabilize the surface of quantum dots. These large molecules hinder the electrons jumping from one quantum dot to the next and so no current flows.

In the new design, the researchers replaced the large molecules with small molecules and filled the empty space between the quantum dots with aluminium oxide. This led to far more contact between the quantum dots allowing the electrons to move freely.

Yield

Using laser spectroscopy the physicists saw that a single photon indeed caused the release of several electrons in the material containing linked quantum dots. All of the electrons that jumped across the band gap moved freely around in the material. As a result of this the theoretical yield of solar cells containing such materials rises to 45%, which is more than 10% higher than a conventional solar cell.

This more efficient type of solar cell is easy to produce: the structure of linked nanospheres can be applied to the solar cell as a type of layered paint. Consequently the new solar cells will not only be more efficient but also cheaper than conventional cells.

The Dutch researchers now want to work with international partners to produce complete solar cells using this design.

Read more at: http://phys.org/news/2013-08-nanomaterial-yield-solar-cells.html#jCpn mobilise several electrons thereby multiplying the amount of current produced.

 

Read more at: http://phys.org/news/2013-08-nanomaterial-yield-solar-cells.html#jCp