Full-Spectrum Solar Cells

[hankthecrank]

http://www.greencarcongress.com/2006/11/rosestreet_labs.html#more

RoseStreet Labs and Sumitomo Chemical Announce JV for Full-Spectrum Solar Cells
2 November 2006

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.

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.

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.

Sounds good but remains to be seen if the rubber meets the road or not.

[eppur_se_muova]

1. Sounds like a real breakthrough. This kind of new thinking has been lurking in the wings, but ...

it's been getting the actual materials engineering ("bandgap engineering") done just right that's been the challenge.

[phantom power]

2. If they can make a full-spectrum PV cell, it also remains to be seen...

how much it costs. If they make a 48% efficient cell, but it costs 4x as much as a typical 12%-efficient cell, the cost/watt doesn't improve.

[Kolesar]

3. Hence, it would be more effective to trade off "area" for "efficiency"

Unless a site was severely constrained for available area. I could see in several years that a commercial building would try to be self-sufficient with just the rooftop PVs.

[FREEWILL56]

4. Old Technology

It's been done and isn't new.
http://www.uni-solar.com/interior.asp?id=66
Where it says this " Click here to view our Technology Report." click on it to see what I'm saying.

I do have 2 of these us64 panels that i bought years ago. they are not very efficient and current technology has allowed cells to be produced with efficiencies of about 20%. the higher the efficiency, the higher the price so does it really matter that much?

[eppur_se_muova]

5. Thanks for that link. Same basic idea, very different materials.

more from article in the OP:

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%.

I've highlighted in bold what may be the most important phrase in the article -- lower mfg cost. The UniSolar materials use Si/SiGe layers, and the multiple layers add to the mfg cost.

Interestingly enough, the article mentions they have another candidate:

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%.