Copper Indium Gallium diSelenide

CIGS (Copper Indium Gallium diSelenide) is a class of thin-film photovoltaic material. The material consists of four thin layers of copper, indium, gallium and diSelenide that, when combined, are about 1/20 of the thickness of a piece of paper. When placed in the sun, electricity is generated by the two center layers. The outer two layers remove electricity from the middle layers similar to the positive and negative terminals of a common battery.

The low-cost process of producing CIGS is similar to that used to deposit reflective coatings on common glass products like eyeglasses, windshields and plate glass.

Of the thin-film technologies, CIGS is considered the best. It has the highest conversion efficiency and, while the conversion efficiency of many photovoltaic materials rapidly deteriorate over time, CIGS tends to be stable. CIGS is also less expensive to manufacture due to lower labor, material, energy, handling and capital costs. Installation is also easier costs of installation lower as a result of compact, lightweight packaging.

Gallium arsenide (GaAs)

Dual-junction cells

Dual-junction cells are approximately 4.2 square inches in area and 0.0055 thick. They can convert over 21% of the sun's light into electricity. They are made efficient by having two solar cells layered on top of each other. Each layer converts a different part of the light spectrum. The top layer, gallium indium phosphide, converts short wavelengths into electrical power. Long wavelengths, transparent to the top gallium indium phosphide layer, pass through to the gallium arsenide layer where they are also converted into electricity. Since sunlight is collected by 2 layers instead of just one, the are called dual-junction cells and have greater efficiency than conventional one layer cells.

Triple-junction cells

An efficient 3-layer cell for space applications. In 2001, this technology achieve a world-record conversion efficiency rate of 34 percent; making it the first solar technology to achieve the U.S. Department of Energy (DoE) One-Third-of-a-Sun initiative. Boeing's Spectrolab collaborated with the National Renewable Energy Laboratory (NREL). Each of the three junctions captures and converts a different portion of the solar spectrum. Designed to withstand the energy of highly concentrated sunlight, they require fewer cells to generate a given amount of power. It is expected that this technology, with improvements could produce electricity at a cost of $0.50 per watt. Spectrolab is capable of making hundreds of megawatts of triple-junction concentrator solar cells per year.