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Copper-indium-gallium-selenide (CIGS) solar cells are a rising star amongst thin-film solar technologies. CIGS cells have long shown promise in the race to develop an efficient low-cost solar cell, reaching efficiencies of nearly 20% in the laboratory. Until recently, however, efficient manufacturing was a major barrier to mass production.
How Do They Work?
All solar cells in commercial use today require a semiconductor material to generate electricity from sunlight. Most cells are differentiated by this material and CIGS is no exception. The copper, indium, gallium and selenide are blended to form a semiconductor layer within the cell. It is within this layer that excited electrons form an electrical current.
Above the CIGS layer in the solar cell are layers of zinc oxide (ZnO) and Cadmium Sulfide (CdS). The zinc oxide acts as the other side of the positive-negative (p-n) junction required to create an electrical current. The cadmium sulfide is a buffer between the CIGS and ZnO. The top two layers have a very wide band gap to allow the photons of solar energy to penetrate through to the CIGS. When the electrons in the semiconductor layer are excited, they are attracted to the "holes" in the ZnO layer, which in an abstract way tricks them out into the open. Here, they are caught like cattle and ushered into the electric current.
As mentioned earlier, a major barrier to widespread production of CIGS solar cells has been the lack of efficient methods for production. Recently, a few companies, most notably Nanosolar, have put inexpensive assembly line-production processes to good use. Nanosolar's breakthrough involves using metal foil (as opposed to glass) as a substrate. The cheap, flexible foil allows Nanosolar to produce their solar cells at an incredibly fast rate using a roll-to-roll method, sort of like a printing press.
With the help of this process, as well as automation, Nanosolar can produce one CIGS-based solar panel every 10 seconds at one-tenth the manufacturing cost of conventional silicon panels. Panel conversion efficiency was independently tested at 11%, just edging out First Solar, world leader and thin-film competitor.
The Nanosolar example is just one of many blossoming in the CIGS sector at present. Solyndra, SunFilm and Q-Cells are just a few other companies focusing on or dabbling in CIGS solar cells, the mass production of which is expected to increase from 32 megawatts in 2007 to 1.3 gigawatts by 2012. If you're not hearing too much about CIGS solar cells as of yet, remember that they are still fairly new to the solar industry. Their massive impact may not become apparent for another few years.Monocrystalline Solar Cells / Amorphous Silicon Solar Cells / Gallium Arsenide Solar Cells / CIGS Solar Cells / Polycrystalline Solar Cells / Copper Indium Selenide Solar Cells
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