Can the Upstarts Top Silicon
Solar Energy - Journal ArticleAuthor: Service, Robert F.
Author Affiliation: Science Magazine
Submitted: Thu, 07/10/2008 - 17:14
Edited: Thu, 07/10/2008 - 17:18
Published in: Science Magazine on February 8th, 2008
Copyright Status: Pay to Download Link to source material: Full Article Here Description:
Silicon solar panels (currently accounting for 90% of the current market) are already approaching their potential peak for converting sunlight into electricity. The most efficient silicon cells on the market can convert 24% of the energy in sunlight to electricity, however most commercial cells achieve 15% to 20% efficiencies.
Given the sun's radiation spectrum, and the band gap of silicon (the energy difference between valence orbitals), only certain red photons have the energy required to excite valence electrons and produce electrical current, resulting in a maximum theoretical photon-to-electricity efficiency of 31% for silicon. This is known as the Shockley-Queisser limit.
This article outlines some of the technologies researchers are developing to boost efficiency. Technologies include: the layering of multiple light absorbing materials with different band gaps designed to capture different fractions of the suns light, the doping of silicon with lead selenide or indium arsenide quantum dots that generate multiple charges each time a photon is absorbed (silicon only generates one charge), the focusing of sunlight with mirrors and lenses to supercharge solar cells, experimenting with light-absorbing plastics or similar organic materials that can be manufactured without the expensive vacuum deposition machines required for most inorganic substrates, the coating of silicon with a layer of silver nanoparticles (encouraging the surface plasmon resonance effect) causing the nanoparticles to act like antennas capturing and funneling energy into the conductor more efficiently, exploring cheaper roll-to-roll processing on thin films of copper indium gallium selenide atop a metal foil, and the nanowireing of electrodes.
The author reminds us that many of the approaches to increasing cell efficiency will require expensive materials and manufacturing techniques, and that capital costs are likely to increase. It is unclear if the increased efficiencies will outweigh the increased costs at this time, however there is no shortage of ideas.
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