Solar ♦ news digest
At top, a test device of the new multiband solar cell was arranged to block current from the intermediate band; this allowed a wide range of wavelengths found in the solar spectrum to stimulate current that flowed from both conduction and valence bands (electrons and holes, respectively). In a comparison device, (see bottom), the current from the intermediate band was not blocked, and it interfered with current from the conduction band, limiting the device’s response.
The results of the test showed that light penetrating the blocked device efficiently yielded current from all three energy bands – valence to intermediate, intermediate to conduction, and valence to conduction – and responded strongly to all parts of the spectrum, from infrared with an energy of about 1.1 electron volts (1.1 eV), to over 3.2 eV, well into the ultraviolet.
By comparison, the unblocked device responded well only in the near infrared, declining sharply in the visible part of the spectrum and missing the highest-energy sunlight. Because it was unblocked, the intermediate band had essentially usurped the conduction band, intercepting low-energy electrons from the valence band and shuttling them directly to the contact layer.
Further support for the success of the multiband device and its method of operation came from tests “in reverse”, operating the device as a light emitting diode (LED). At low voltage, the device emitted four peaks in the infrared and visible light regions of the spectrum.
Primarily intended as a solar cell material, this performance as an LED may suggest additional possibilities for gallium arsenide nitride, since it is a dilute nitride very similar to the dilute nitride, indium gallium arsenide nitride, used in commercial “vertical cavity surface-emitting lasers” (VCSELs), which have found wide use because of their many advantages over other semiconductor lasers.
With the new, multiband photovoltaic device based on gallium arsenide nitride, the research team has demonstrated a simple solar cell that responds to virtually the entire solar spectrum and can readily be made using one of the semiconductor industry’s most common manufacturing techniques. The scientists say these results promise highly efficient solar cells that are practical to produce.
Further details of this work are published in the paper, “Engineering the Electronic Band Structure for Multiband Solar Cells,” by Nair Lopez, Lothar Reichertz, Kin Man Yu, Ken Campman, and Wladyslaw Walukiewicz, Phys. Rev. Lett. 106, 028701 (2011).
Sulfurcell Secures €18.8m Funding for CIGSe Market Expansion
Intel Capital has rounded up a number of investors to promote the firm’s thin-film technology for solar modules targeted at the BIPV, solar construction and commercial rooftop sectors.
Sulfurcell, a leader in CIGS/CIGSe type thin-film solar modules, has secured € 18.8m (US $ 25m) in equity funding for the expansion and market introduction of its second generation thin-film photovoltaic (PV) technology.
CIGSe materials provide a promising new technology for PV modules which can deliver the same performance as conventional modules at half the cost. Since producing and shipping its first modules to customers in 2005, Sulfurcell has successfully commercialized on a mass scale, ramping-up its 35 MW facility fabrication. The firm has developed unique, comprehensive solutions for the BIPV, solar construction and commercial rooftop sectors.
The funding comes on the heels of Sulfurcell’s recent accomplishment of manufacturing full scale thin-film modules with 12.6 % efficiency. The firm’s realization of the high-efficiency potential of CIGSe-type modules in an industrial production environment confirms the company’s position as one of the leading companies in CIGS/CIGSe technology.
Sulfurcell’s investors have funded the acquisition of additional CIGSe equipment and ongoing R&D work targeting 14% efficiency within the next 12 to 18 months.
The financing round was led by Intel Capital, the global investment arm of Intel Corporation. Intel was joined by a group of leading European and US
January / February 2011
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