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RoseStreet Labs and Sumitomo Chemical Announce JV for Full-Spectrum Solar Cells

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!)






Te - Tellurium, one of the rarest of earth elements. I hope these cells don't need very much of this stuff or you won't build very many. Can these cells work at high temperatures so that you can use light condensers.


Read the Resources link. The other semicondutor compound is InGaN.


There's not a whole lot of Indium around either and a number of other solar chemistries rely on Indium.

Roger Davis

Although it' strue that many of these more exotic panels are based on rare elements, the nanoscience behind most of these technologies seems quite promising and still in its infancy. My guess is that by the time they start running out of whatever-ium 20 years from now they will be working with different and hopefully much more common elements. The current CIGS stuff used by Nanosolar et al. may not be the ultimate PV of the future but it will hopefully lead the way there -- it doesn't seem like any other approach is as likely to do that, IMHO.


I remember Boris and Natasha used upsidasium for the hushaboom..but that was another story :)

Robert Schwartz

Efficiency is not the real solar problem. The real problems are 1. cost -- the cost of solar cells is still an order of magnitude too high to be economic, and 2. It is 11:22 p.m. as I write this -- the yield on solar cells in this town is 0.

Thomas Pedersen

Robert Schwartz wrote:

It is 11:22 p.m. as I write this -- the yeild on solar cells in this town is 0.

- which is why you should charge your PHEV during daylight (at the company parking lot). The same goes for airconditioning (slush ice thermal storage) and warm water, so the wind turbines/geothermal/nuclear only has to run you computer, TV, lighting etc. after sunset.

But you are right, efficiency is not the problem of solar energy, it is cost.

Speaking of charging you car while at work, I saw that North Island Naval Air Station, San Diego, CA has a 750 kW PV system that is place on the parking lot, thus providing shade for the cars. A great two-for-one Solution:


The Earth is estimated to contain about 0.1 ppm of indium which means it is about as abundant as silver


Use concentrator systems, 1-1000, or greater. Dishes, and mirrors.


Perhaps lenses and prisms too. This setup would be able to use multiple, single layered/compound chips.


As I recall, there is enough Indium to provide less than 5% of the worlds energy. While that IS a lot, it shows the limitations.


I'm in no way implying that we should not pursue these PV panels just because they use rare earth elements. These are just part of a whole suite of solutions that will each find it's place.


Like carbon quantum dots, or concentrator arrays that use 1000K heat engines w/ H2 or liquid Sodium (perhaps liquid calcium for higher operating temps).


Indium is used for LCD displays, so increased demand might drive up price and create shortages. I would like to see all the PV makers succeed, but everyting has its limits.


When there is a need, there is (eventually) a way. LCDs may eventually be replaced by other thecnology, like OLEDs. It is only the matter of time, brains, and capital to be invested in the basic science, and R&D of these fields.


There MAY eventually be a way. I was pointing out the supply/demand function. In the short haul demand could exceed supply. In the long haul, you run out of supply entirely. Sure, keep thinking "outside the box", but everything has its limits.


"everything has limits"
This is exactly one the underlying reason the Hydrogen economy is being persued. There is so much of it on the planet, and in the universe, that the US politician (and others) expousing it do not have to ask citizens (developed world) to reconsider their consumption driven society (esp US). To a certain extent, this is also true with Nuclear Fusion. They get to say you CAN have the cake, AND eat it.


In the westward movement in America, everything seemed limitless. When the oil embargo hit in the 70s people were jolted into the idea of limits. Some politicians played to the people wanting to believe in a limitless future, infortunately too many believed them.


full spectrum may be created though quantum dot materials i heard there is options more than one of about a dozen likely these fields are how not why.there is also a rull specturm infra red metal for multi uses, wil;l you dont you think.


plus mirror nano technotogy may split spectra materials

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