Researchers demonstrate ‘avalanche effect’ in solar cells

Friday, 27 June, 2008

Proof that the ‘avalanche effect’ by electrons occurs in specific, very small semiconducting crystals could pave the way for cheap high-output solar cells.

Researchers at TU Delft and the FOM Foundation for Fundamental Research on Matter have discovered this phenomenon.

Solar cells provide opportunities for future large-scale electricity generation. However, there are currently significant limitations, such as the relatively low output of most solar cells (typically 15%) and high manufacturing costs.

One possible improvement could develop from a solar cell made of semiconducting nanocrystals which could lead to theoretical maximum output of 44%.

In conventional solar cells, one photon can release precisely one electron. The creation of these free electrons ensures that the solar cell works and can provide power.

The more electrons released, the higher the output of the solar cell.

In some semiconducting nanocrystals, however, one photon can release two or three electrons, hence the term 'avalanche effect'.

The avalanche effect was first measured by researchers at the Los Alamos National Laboratories in 2004. Since then, the scientific world has raised doubts about the value of these measurements. Does the avalanche effect really exist or not?

Within the Joint Solar Programme TU Delft’s Prof Laurens Siebbeles has now demonstrated that the avalanche effect does indeed occur in lead selenide (PbSe) nanocrystals.

It has been established, however, that the effect in this material is smaller than previously assumed. Siebbeles claims his results are more reliable than those of other scientists due to more careful and more detailed measurement using ultra-fast laser methods.

Siebbeles believes that this research paves the way for further unravelling the secrets of the avalanche effect.


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