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Not Transparent Aluminum, But Conductive Plastic
michaelmalak writes "Scientists at the US Department of Energy's Brookhaven National Laboratory and Los Alamos National Laboratory have fabricated transparent, thin films capable of absorbing light and generating electric charge over a relatively large area. The material, described in the journal Chemistry of Materials (subscription required), could be used to develop transparent solar panels or even windows that absorb solar energy to generate electricity. The material consists of a semiconducting polymer doped with carbon-rich fullerenes."
It's transparent because the film has a hexagonal structure - extremely thin (and therefore transparent) at the center of the hexagon, thick (and therefore opaque) at the edges of the hexagons. The electricity is generated at the edges, as that is where the light is absorbed and that's where all the electrons are ready to be knocked off their molecules. It's not blocking certain wavelengths and allowing others through (well obviously to some degree it is, but not in the visible spectrum). It's blocking light in certain parts and allowing light through in others.
It's basically going to tint the windows, how much will be determined by how densely the hexagons are packed - more hexagons means more electricity but also a darker tint.
Security is mostly a superstition... Avoiding danger is no safer in the long run than outright exposure. - Helen Keller
It's transparent because the film has a hexagonal structure - extremely thin (and therefore transparent) at the center of the hexagon, thick (and therefore opaque) at the edges of the hexagons.
Actually it's a little bit more interesting than that. In addition to being thinner at the center, the light-absorbing polymer is not well-ordered (amorphous) in the center region, which leads to it being worse at absorbing light. At the edges of the hexagons, the polymer orders better, which allows it to absorb light more efficiently. This makes the structure more intelligent, in principle: if the honeycomb structure acts as one half of the conduction pathway (necessary for a photo-voltaic), then it makes sense to have the material close to it do the light-absorbing, and have the material further away (center of hexagons) which cannot participate in light harvesting, just be transparent. So this in principle allows one to design more efficient semi-transparent solar cells.
Peeling back the layers of hype a bit, however, these kinds of solar cells are horribly inefficient. The best materials we currently have to make plastic solar-cells ("organic photo-voltaics") have pretty poor efficiency. Making a solar cell that's semi-transparent just makes the efficiency (per unit area) even worse. But, this is fairly fundamental research: by demonstrating that they can tune the light-absorbing capabilities of the polymer based on its ordering (and control ordering by using the honeycomb patterning and preparation parameters), this provides useful information about how to make higher-performance plastic solar-cells. So this research may actually end up being more important for conventional solar cells ('opaque') than it is for window-coating solar-cells or whatever.
P.S.: The materials used in the paper have an absorption maximum at 503 nm (green), so they probably create a purplish tint. The absorption spectrum can be tuned to change the tint, however this will impact the solar collection efficiency.
Disclaimer: Some of the co-authors are colleagues of mine. However I wasn't involved in this work in any way.
What's really going on in solar is that big US companies with real manufacturing expertise are moving in.
This is where the action is. Solar is a heavy-manufacturing business, and it's the companies with experience in running big factories that are now taking over.