Solar power heads in a new direction: thinner

[OKIsItJustMe]

http://web.mit.edu/newsoffice/2013/thinner-solar-panels-0626.html

[font face=Serif][font size=5]Solar power heads in a new direction: thinner[/font]
[font size=4]Atom-thick photovoltaic sheets could pack hundreds of times more power per weight than conventional solar cells.[/font]

David L. Chandler, MIT News Office
June 26, 2013

[font size=3] Most efforts at improving solar cells have focused on increasing the efficiency of their energy conversion, or on lowering the cost of manufacturing. But now MIT researchers are opening another avenue for improvement, aiming to produce the thinnest and most lightweight solar panels possible.

Such panels, which have the potential to surpass any substance other than reactor-grade uranium in terms of energy produced per pound of material, could be made from stacked sheets of one-molecule-thick materials such as graphene or molybdenum disulfide.

Jeffrey Grossman, the Carl Richard Soderberg Associate Professor of Power Engineering at MIT, says the new approach “pushes towards the ultimate power conversion possible from a material” for solar power. Grossman is the senior author of a new paper describing this approach, published in the journal Nano Letters.

…

Using two layers of such atom-thick materials, Grossman says, his team has predicted solar cells with 1 to 2 percent efficiency in converting sunlight to electricity, That’s low compared to the 15 to 20 percent efficiency of standard silicon solar cells, he says, but it’s achieved using material that is thousands of times thinner and lighter than tissue paper. The two-layer solar cell is only 1 nanometer thick, while typical silicon solar cells can be hundreds of thousands of times that. The stacking of several of these two-dimensional layers could boost the efficiency significantly.

…[/font][/font]

[BlueStreak]

1. I'm not sure energy-per-pound is an important metric

It could be important in niche applications, like satellites. Anything to reduce the payload is a good thing in that instance.

But even if there aren't many obvious applications today, this seems like important basic research.

[OKIsItJustMe]

2. Roofs come to mind

Less weight would mean less structural strength is required.

[BlueStreak]

3. Possibly, but not at 1/5 the efficiency

If they can develop this to the point that it is almost as efficient as conventional PV, then certainly it becomes interesting.

[OKIsItJustMe]

4. “Stacking” should help

http://pubs.acs.org/doi/abs/10.1021/nl401544y

… We further suggest that given the variability of band gaps observed in TMD monolayers, usually in the 1.5?2.5 eV range and decreasing for increasing sizes of the chalcogen atom, significant band gap engineering is possible using stacked TMD bilayers and multilayers. This scenario entails novel possibilities to form broadband sunlight absorbers and enhance efficiency considerably beyond the values estimated here. …

[BlueStreak]

5. A PV sandwich

That is promising. This is similar to the dual-layer CD technology, although that involves a lens to focus the laser on the desired layer.

I wonder if there is more energy available than has been considered to date -- this notion of "broad spectrum" absorbers. Plants are mostly green because that is the optimal wavelength to absorb the most energy. But sunlight is not just in the green wavelength. Maybe this technology could lead to dozens of layers, each optimized to capture energy from other wavelengths. That is what they are suggesting. I wonder if that could fundamentally expand the amount of potential solar energy available, or has this always been part of the efficiency calculation?

[OKIsItJustMe]

6. Others have looked at this with conventional PV

Different chemistries have different response bands:
http://www.nrel.gov/docs/legosti/fy97/22969.pdf


So, how about multiple layers, to get greater overall efficiency?

[BlueStreak]

8. If they need 10 layers to get back to the efficiency of today's PVs I'm not sure I see the benefit.

But if they can customize each layer to capture energy from different bands, then theoretically they might be able to achieve more efficiency than today's PVs.

[quadrature]

7. useful lifetime is?

a typical problem for non-crystal type
solar PV is that it only works for six months.

[BlueStreak]

9. Well, maybe if they combined a lot of layers, that would provide some redundancy

That is a little like solid state disks. There is a finite number of write cycles before each cell is no longer usable, so manufacturers include extra cells that can take over as the first ones wear out.

[OKIsItJustMe]

10. Graphene is incredibly strong

https://en.wikipedia.org/wiki/Graphene#Mechanical