|The intermediate band allows absorption of photons at three different energy levels, corresponding to the three different band gaps. In particular, low-energy photons are captured that would pass through a conventional solar cell. Click to enlarge.|
RoseStreet Labs, LLC and Sumitomo Chemical Co., Ltd. (Sumitomo) have formed a joint venture, RSL Energy, Inc., for the development and manufacturing of full-spectrum solar cells. The joint venture will be headquartered in Phoenix, Arizona.
RSL Energy will commercialize next-generation technology utilizing full-spectrum solutions that can potentially achieve practical efficiencies above 48% in both single junction and multi-junction devices.
RSL Energy has exclusive patent licenses from both Lawrence Berkeley National Laboratory (Berkeley Lab) and Cornell University for unique semiconductor devices that use a significantly larger fraction of the solar spectrum compared to existing products.
RSL Energy will commercialize Berkeley Lab’s multi-band technology which incorporates a unique new semiconductor material that can achieve the efficiencies of a triple junction device with the manufacturing cost and simplicity of a single junction device.
Developed by a research team led by Kin Man Yu and Wladek Walukiewicz, the Berkeley technology uses a new ZnMnTe semiconductor material with multiple energy gaps. This type of multiband semiconductor had been theoretically predicted but never before made, and the work won the R&D 100 Award in September of this year and the R&D 100 Award for Most Promising Technology in October of this year.
The power conversion efficiency limit for a solar cell employing a single semiconducting material is 31%. The primary basis of this limit is that no single material can absorb light across the full range of solar radiation, which has usable energy in the photon range of 0.4 – 4 eV (infrared to ultraviolet). Light with energy below the bandgap of the semiconductor will not be absorbed and thus not be captured for energy conversion. Light with energy above the bandgap will be absorbed, but the excess energy above the bandgap will be lost in the form of heat. Decades of research in developing single-material solar cells has led to cell efficiencies close to the theoretical limit; the best cell of this type has an efficiency of 25.1%.
To address this, the researchers Wladyslaw Walukiewicz and Kin Man Yu split the conduction band of a semiconductor compound (ZnMnTe) by adding oxygen to the semiconductor alloy. The resulting material becomes multi-band, with energy transitions that fall within the range of the solar spectrum.
Theoretically, the triple-band material can achieve an ideal power conversion efficiency of 56%—a figure the researchers think they could push to 73% calculated efficiency with a quad-band semiconductor.
In addition, RSL Energy is also commercializing the InGaN multi-junction technology of Cornell and Berkeley Lab, which is expected to provide outstanding thermal and radiation properties necessary for next-generation concentrator-based photovoltaics (CPVs) utilized in distributed energy power generation. RSL Energy believes that the InGaN cells could achieve efficiencies of more than 48%.
RSL Energy will perform R&D and product development during 2007 and expects to have its first prototypes for field testing in 2008 in the CPV distributed energy, flat panel, space and architectural applications. RSL Energy will leverage RoseStreet Labs’ Phoenix-based R&D Laboratory and its high volume semiconductor bumping foundry, FlipChip International, to produce a competitive entry for full spectrum solar cells into the rapidly growing global renewable energy market.
We are very proud to have Sumitomo Chemical as our partner in this solar energy venture. With our strategic relationship with Sumitomo Chemical and the Berkeley Lab and Cornell breakthroughs in photovoltaic devices, we plan to leapfrog advances in solar cell applications. We believe RSL Energy can provide a unique product solution for a broad range of renewable energy applications - at a cost of ownership close to prevailing utility rates. Full Spectrum technology also has the potential for products to be supplied on a variety of substrates thereby enabling creative applications in the architectural, wireless, automotive, rooftop/shingle, and distributed energy industries. We are also proud to have Dr. Wladek Walukiewicz, innovator of multi-band technology and our Chief Technology Officer for RSL Energy, to drive the technology development of full spectrum solutions for the global photovoltaic markets.—Bob Forcier, President and CEO of RoseStreet Labs
RoseStreet Labs, LLC, is a supplier of products and services in the life sciences, renewable energy and homeland security markets.
(A hat-tip to Allen!)
“Solar power venture focuses on ZnMnTe and InGaN” (Compound Semiconductor.net)