Berkeley Lab Develops Technology To Make Photovoltaics Out of Any Semiconductor

First time accepted submitter bigvibes writes "A technology that would enable low-cost, high efficiency solar cells to be made from virtually any semiconductor material has been developed by researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley. This technology allows for plentiful, relatively inexpensive semiconductors, such as metal oxides, sulfides and phosphides that had previously been considered unsuitable for solar cells because of the difficulty in tailoring their properties by chemical means."

*yawn*

[sycodon]

call me when I can buy it in rolls or sheets at Home Depot.

Re:Acronym abuse

[Samantha Wright]

There's an easy explanation for that: the second "E" disappears when you say it quickly (ess ee fee ee pee vee), and the first one would make the initialism long and unwieldy without providing pronounceability. "PV" describes the root noun and hence is more important to the meaning of the term, and makes it easier to infer what the abbreviation describes when scanning snippets of unfamiliar literature. Irregularity in such contractions is not a new thing, though—ever seen "Wm." for "William"?

Brevity, especially the minimum effort to provide disambiguation, supersedes consistency; otherwise we wouldn't use abbreviations at all. Think of it like Huffman coding. Huffman coding is the wellspring of life.

An article with a diagram

[purpledinoz]

It's really hard to picture what is described in the article. Here's a link to an article with a diagram. [lbl.gov]

Attempt at layman explanation

[LourensV]

I read the article (I know! But there were no comments yet, so what am I to do?) and, not having understood much of it, did some reading to try and understand what's going on here. I think I've more or less figured it out, so I'm attempting a simple explanation here. Semiconducting physics nerds, please fix this for me as appropriate.

Atoms consist of a positively charged nucleus, surrounded by one or more shells of electrons. Electrons farther away from the nucleus have more energy than ones closer in. Put a bunch of those atoms together, and there are two things that can happen. In some materials, the electrons in the higher energy states are so "far away" from the nucleus in energetic terms, that they can easily move from one atom to the next. These materials are conductors. In other materials, there is a big gap (the band gap) between the highest "bound" (valence band) energy state, and the minimum energy state (the conduction band) needed to move between atoms. So, the electrons can't move away from their nuclei, and these materials are electrical insulators. Then there are some materials that have an intermediate sized gap between stuck valence states and free-to-move conduction states, and these are called semiconductors.

A solar cell works by the photoelectric effect: when an incoming photon (e.g. sunlight) hits an electron in a semiconductor, the electron absorbs the photon and its energy increases. If the photon is energetic enough, this will move the electron from the valence band to the conduction band. This also creates a positively charged "hole", where the electron was before. The electron and the hole attract each other because they have opposite charge. Left to their own devices, they'll just recombine, so in a solar cell, an electric field is applied. This moves the electron in one direction, and the hole in the opposite direction (because of the opposite charge). This moving electrical charge is otherwise known as current flow, and so we have a working solar cell.

So how do we make an electric field? In normal photovoltaic cells, this is done by doping (adding small impurities, typically boron and phosphorus to) the semiconductor. Since these have less or more electrons in their outer shells, they create areas in the semiconductor with more electrons or more holes, which creates a charge difference between them (a P-N junction). This charge difference creates an electric field, which will whisk away any electrons and holes created within it. Apparently, this doping process only works for relatively expensive semiconductors however.

So, if I understand correctly, what these researchers have done is to apply an external electric field, by applying a small voltage across the whole thing. This puts a charge on the contacts on each side of the cell, which draws electrons in the semiconductor one way and holes the other way, thus creating a P-N junction without doping. The problem is that normally the construction of the contacts keeps their electric field from propagating into the semiconductor, so that it doesn't generate a good P-N junction. Apparently they've overcome this by changing the geometry of one of them, in two different ways for two different alternative semiconductors. And then they have a version in which the external voltage is supplied by the cell itself, making it self-contained.

So is this useful? Well, conspicuously absent from the article is any mention of efficiency. So I'd speculate that this mainly allows the production of low-efficiency solar cells at lower prices than before, rather than getting more output from your roof. But if this makes solar cells cheap enough to just blanket anything and everything with them, that could still be useful of course.

Re:Available 5 years from now

[timeOday]

That is approximately true [scientificamerican.com]. A 95% reduction in price over 30 years is pretty darn impressive. Not all at once, of course, but the accumulation of dozens of such advances.