"Avalanche effect" research promises greater solar cell efficiency
By Emily Clark
May 27, 2008
Research continues to improve efficiency in solar cells, whilst simultaneously finding ways to lower the costs of module production. The latest research surrounds the use of semiconducting nanocrystals (crystals with dimensions in the nanometer size range) and the “avalanche effect” created when they are exposed to sunlight.
To create solar power, photons (light particles) in sunlight hit a solar panel and free electrons from their atoms to produce electricity. Unlike conventional cells that release only one electron per photon, some semiconducting nanocrystals have the ability to release two or three electrons per photon. This phenomenon is referred to as the “avalanche effect” and has the potential to lead to a maximum output of 44% (the average output of current solar cells is around 15%) in a solar cell made up of semiconducting nanocrystals. The other attractive property of these types of cells is that they can be manufactured relatively cheaply, meaning the technology could pave the way for low-cost, high-output solar cells.
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. In this recent announcement, researchers at TU Delft and the FOM Foundation for Fundamental Research on Matter led by Prof. Laurens Siebbeles claim to have found irrefutable proof that the so-called avalanche effect by electrons does actually occur in lead selenide (PbSe) nanocrystals. However, the effect in this material is smaller than previously assumed, but Siebbeles believes that this research will lead to further discoveries relating to the phenomenon. The findings from the researchers have been published in scientific journal Nano Letters.
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