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Mobile electrons multiplied in quantum dot films

Date:
October 17, 2011
Source:
Delft University of Technology
Summary:
Researchers have demonstrated that several mobile electrons can be produced by the absorption of a single light particle in films of coupled quantum dots. These multiple electrons can be harvested in solar cells with increased efficiency.
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Credit: Image courtesy of Delft University of Technology

Researchers of the Opto-electronic Materials section of the TU Delft and Toyota Europe have demonstrated that several mobile electrons can be produced by the absorption of a single light particle in films of coupled quantum dots. These multiple electrons can be harvested in solar cells with increased efficiency.

The researchers published their findings in the October issue of the scientific journal Nano Letters.

A way to increase the efficiency of cheap solar cells is the use of semiconductor nanoparticles, also called quantum dots. In theory, the efficiency of these cells can be increased to 44%. This is due to an interesting effect that efficiently happens in these nanoparticles: carrier multiplication. In the current solar cells, an absorbed light particle can only excite one electron, while in a quantum dot solar cell a light particle can excite several electrons. Multiplying the number of electrons results in the enhancement of current in solar cells, increasing the overall power conversion efficiency.

Carrier Multiplication

Several years ago it was demonstrated that carrier multiplication is more efficient in quantum dots than in traditional semiconductors. As a result, these quantum dots are currently heavily investigated worldwide for use in solar cells. A problem with using carrier multiplication is that the produced charges live only a very short time (around 0.00000000005 s) before they collide with each other and disappear via a decay process known as Auger recombination. The main current challenge is to proof that it is still possible to do something useful with them.

Mobile charges

The researchers from Delft have now demonstrated that even this very short time is long enough to separate the multiple electrons from each other. They prepared films of quantum dots in which the electrons can move so efficiently between the quantum dots that they become free and mobile before the time it takes to disappear via Auger recombination. In these films up to 3.5 free electrons are created per absorbed light particle. In this way, these electrons do not only survive, they are able to move freely through the material to be available for collection in a solar cell.


Story Source:

The above post is reprinted from materials provided by Delft University of Technology. Note: Materials may be edited for content and length.


Journal Reference:

  1. Michiel Aerts, C. S. Suchand Sandeep, Yunan Gao, Tom J. Savenije, Juleon M. Schins, Arjan J. Houtepen, Sachin Kinge, Laurens D. A. Siebbeles. Free Charges Produced by Carrier Multiplication in Strongly Coupled PbSe Quantum Dot Films. Nano Letters, 2011; 11 (10): 4485 DOI: 10.1021/nl202915p

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Delft University of Technology. "Mobile electrons multiplied in quantum dot films." ScienceDaily. ScienceDaily, 17 October 2011. <www.sciencedaily.com/releases/2011/10/111014080041.htm>.
Delft University of Technology. (2011, October 17). Mobile electrons multiplied in quantum dot films. ScienceDaily. Retrieved July 31, 2015 from www.sciencedaily.com/releases/2011/10/111014080041.htm
Delft University of Technology. "Mobile electrons multiplied in quantum dot films." ScienceDaily. www.sciencedaily.com/releases/2011/10/111014080041.htm (accessed July 31, 2015).

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