Solar cells are semiconductor devices that convert light to electricity. They have many applications. They have long been used in situations where electrical power from the grid is unavailable, such as in remote area power systems, Earth-orbiting satellites and space probes, consumer systems, e.g. handheld calculators or wrist watches, remote radiotelephones and water pumping applications. More recently, they are starting to be used in assemblies of solar modules connected to the electricity grid through an inverter, often in combination with net metering.

Solar cells are regarded as one of the key technologies towards a sustainable energy supply.

Three generations of development

First
The first generation photovoltaic consists of a large-area, single layer p-n junction diode, which is capable of generating usable electrical energy from light sources with the wavelengths of sunlight. These cells are typically made using a silicon wafer. First generation photovoltaic cells (also known as silicon wafer-based solar cells) are the dominant technology in the commercial production of solar cells, accounting for more than 86% of the solar cell market.

Second
The second generation of photovoltaic materials is based on the use of thin-film deposits of semiconductors. These devices were initially designed to be high-efficiency, multiple junction photovoltaic cells. Later, the advantage of using a thin-film of material was noted, reducing the mass of material required for cell design. This contributed to a prediction of greatly reduced costs for thin film solar cells. Currently (2007) there are different technologies/semiconductor materials under investigation or in mass production, such as amorphous silicon, poly-crystalline silicon, micro-crystalline silicon, cadmium telluride, copper indium selenide/sulfide. Typically, the efficiencies of thin-film solar cells are lower compared with silicon (wafer-based) solar cells, but manufacturing costs are also lower, so that a lower price in terms of $/watt of electrical output can be achieved. Another advantage of the reduced mass is that less support is needed when placing panels on rooftops and it allows fitting panels on light materials or flexible materials, even textiles. This allows for portable roll-up solar panels, which can fit in a backpack and be used to power cell phones or laptops in remote areas.

Third
Third generation photovoltaics are very different from the other two, broadly defined as semiconductor devices which do not rely on a traditional p-n junction to separate photogenerated charge carriers. These new devices include photoelectrochemical cells, Polymer solar cells, and nanocrystal solar cells.

Companies working on third generation photovoltaics include Xsunx, Konarka Technologies, Inc., Nanosolar and Nanosys. Research is also being done in this area by the USA's National Renewable Energy Laboratory (http://www.nrel.gov/).

Notes

 
 PVNET European Roadman for PV R&D  Ed Arnulf Jager-Waldan Office for Publications of the European Union 2004

Other websites 

Directory of Solar Cell Manufacturers 
Directory of Solar Cell Manufacturing Equipment Suppliers 
School of Photovoltaic and Renewable Energy Engineering (Research lab of Prof. Martin Green et al.)
Energex: Animation of how a solar cell works 
Carbon Nanotube Solar Cells  (28 February 2005)
Flexible Silicon Solar Cells (15 February 2003)
Historical: Photovoltaic Solar Energy Conversion: An Update (M. Green, 1998)
Howstuffworks.com: How Solar Cells Work
Organic Photovoltaics and Materials — Overview 
Organic Solar Cells for the Near-Infrared Spectrum 
Photovoltaic Residential Benefits 
Photovoltaic Solar Panel Overview
Photovoltaic Thin Films for the Full Solar Spectrum  (W. Walukiewicz 2002)
Pliable solar cells are on a roll 
Điện mặt trời Địa Cầu Xanh 
Superefficient, Cost-Effective Solar Cell Breaks Conversion Records - 40.7 percent efficiency achieved (Scientific American, December 2006)

Do-it-yourself
PEC (Photo Electro Chromic)
How to Build Your Own Solar Cell 
DIY (Do It Yourself): Nanocrystalline Dye-Sensitized Solar Cell Kit Quote: "... sunlight-to-electrical energy conversion efficiency is between 1 and 0.5%..."

Cuprous oxide solar cells
Make a Solar Cell in Your Kitchen, A Flat Panel Solar Battery

Newsgroups
alt.solar.photovoltaic

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