Solar cells are used to convert solar or radiant energy into electricity. Historically, solar power (both in space and terrestrially) has been predominantly provided by silicon solar cells. In the past several years, however, high-volume manufacturing of high-efficiency III-V multijunction solar cells has enabled the consideration of this alternative technology for terrestrial power generation.
Compared to Si, III-V multijunction cells are generally more radiation resistant and have greater energy conversion efficiencies, but they tend to cost more. Some current III-V multijunction cells have energy efficiencies that exceed 27%, whereas silicon technologies generally reach only about 17% efficiency. Under concentration, some current III-V multijunction cells have energy efficiencies that exceed 37%. When the need for very high power or smaller solar arrays are paramount in a spacecraft or other solar energy system, multijunction cells are often used instead of, or in hybrid combinations with, Si-based cells to reduce the array size.
Emcore Solar Power, Inc. (Albuquerque, NM) has developed solar cell receivers that include a III-V compound semiconductor multijunction solar cell. Each cell may also include a bypass diode coupled with the solar cell. At least one optical element may be positioned above the solar cell to guide the light from one of the lenses onto the solar cell. Each of said solar cell receivers may be disposed in an optical path of one of the lenses. The lens and the at least one optical element may concentrate the light onto the respective solar cell by a factor of 1000 or more to generate in excess of 25 watts of peak power according to inventors Sunil Vaid, Mikhail Kats, Gary Hering, Philip Blumenfeld, Damien Buie, John Nagyvary, James Foresi and Peter Allen Zawadzki in U.S. Patent Application
Generally speaking, the multijunction cells are of n-on-p polarity and are composed of InGaP/(In)GaAs/Ge compounds. III-V compound semiconductor multijunction solar cell layers can be grown via metal-organic chemical vapor deposition (MOCVD) on Ge substrates. The use of the Ge substrate permits a junction to be formed between n- and p-Ge. The solar cell structures can be grown on 100-mm diameter (4 inch) Ge substrates with an average mass density of about 86 mg/ cm2. In some processes, the epitaxial layer uniformity across a platter that holds 12 or 13 Ge substrates during the MOCVD growth process is better than 99.5%.
Each wafer typically yields two large-area solar cells. The cell areas that are processed for production typically range from 26.6 to 32.4 cm2. The epi-wafers can be processed into complete devices through automated robotic photolithography, metallization, chemical cleaning and etching, antireflection (AR) coating, dicing, and testing processes. The n- & p-contact metallization is typically comprised of predominately Ag with a thin Au cap layer to protect the Ag from oxidation. The AR coating is a dual-layer TiOx/Al2O3 dielectric stack, whose spectral reflectivity characteristics are designed to minimize reflection at the coverglass-interconnect-cell (CIC) or solar cell assembly (SCA) level, as well as, maximizing the end-of-life (EOL) performance of the cells.
A triple-junction III-V compound semiconductor solar cell can be employed, but other types of solar cells could be used depending upon the application. The solar cells may be made from, e.g., silicon (including amorphous, nanocrystalline, or protocrystalline), cadmium telluride, CIGS (copper indium gallium diselenide), CIS (chalcopyrite films of copper indium selenide (CuInSe2)), gallium arsenide (e.g., GaAs multijunctions), light absorbing dyes (e.g., ruthenium metalorganic dye), or organic semiconductors (e.g., polyphenylene vinylene, copper phthalocyanine or carbon fullerenes).
Solar energy is one technology for power generation that is clean, quiet and renewable. It is also plentiful: with an average of roughly 125,000 terawatts of solar energy reaching the planet at any given time, solar technology can potentially generate a significant amount of energy.
On January 27, 2010, EMCORE Corporation, a leading provider of compound semiconductor-based components, systems and subsystems for the fiber optic and solar power markets, reported it had been awarded a contract by ATK Space Systems of Goleta, California to manufacture, test, and deliver solar panels for ATK's UltraFlex™ solar arrays.
These solar arrays will be used to power the Orion spacecraft being developed by Lockheed Martin Space Systems Company for NASA. The period of performance for this contract for the first two vehicles runs through 2013 and is valued in the range of $9-$11 million. The flight solar array system is expendable for each Orion mission and continuous production is expected to run through 2020 and beyond.
The Orion crew exploration vehicle (CEV) program will serve as NASA's next generation human space transportation system. This vehicle is intended to replace the current Space Shuttle and will provide human space flight systems capable of transferring astronauts to and from the International Space Station (ISS), the Moon and other destinations within the solar system. NASA expects to order multiple Orion Constellation vehicles over the next decade.
Emcore's latest generation ZTJ triple-junction solar cells will be designed into the solar panels delivered to ATK Space Systems. With a sunlight-to-electricity conversion efficiency of 30%, the ZTJ solar cell is the highest performance space qualified multi-junction solar cell available in the world today. Production of the solar panels will take place at EMCORE's state-of-the-art manufacturing facilities located in Albuquerque, New Mexico.
On February 9th, EMCORE reported revenue for the first quarter of fiscal 2010 ended December 31, 2009 was $42.4 million, an increase of $1.9 million, or 5%, from $40.5 million reported in the immediately preceding quarter ended September 30, 2009.
On a segment basis, revenue for the Photovoltaics segment was $16.8 million, an increase of $0.4 million, or 3%, from $16.4 million reported in the immediately preceding quarter with the increase due to a 14% increase in revenue from satellite solar power products offset by a decrease in revenue from terrestrial concentrated photovoltaic (CPV) products. The Photovoltaics segment accounted for 40% of the Company's consolidated quarterly revenue for both the three months ended December 31, 2009 and September 30, 2009.
Revenue for the Fiber Optics segment was $25.6 million, an increase of $1.5 million, or 6%, from $24.1 million reported in the immediately preceding quarter with the increase concentrated primarily in the Company's cable television (CATV) product lines. The Fiber Optics segment accounted for 60% of the Company's consolidated quarterly revenue for both the three months ended December 31, 2009 and September 30, 2009.
Emcore Corporation (NASDAQ: EMKR) offers a broad portfolio of compound semiconductor-based products for the broadband, fiber optic, satellite and solar power markets. EMCORE's Fiber Optic segment offers optical components, subsystems and systems for high speed data and telecommunications networks, cable television (CATV) and fiber-to-the-premises (FTTP). Emcore's Photovoltaic segment provides products for both satellite and terrestrial applications. For satellite applications, EMCORE offers high efficiency Gallium Arsenide (GaAs) solar cells, Covered Interconnect Cells (CICs) and panels. For terrestrial applications, Emcore is adapting its high-efficiency GaAs solar cells for use in solar concentrator systems.
For further information about EMCORE, visit http://www.emcore.com.