[Graeme]

Conductivity is More Than Skin Deep

$this->bbcode_second_pass_quote('', 'A') team of researchers from Berkeley Lab's Materials Sciences Division (MSD), led by Wladek Walukiewicz and working with colleagues from Cornell University, has made a form of the semiconductor indium nitride that can conduct positive charges. For any other semiconductor the news would be unremarkable. But indium nitride is one of the most frustrating, if most promising, of semiconductor materials.

Even more promising, when alloyed with gallium nitride, another group III nitride (group III of the periodic table includes aluminum, gallium, indium, and other elements having three valence electrons), indium nitride holds out the possibility of making extraordinary solar cells. Gallium nitride has a band gap of 3.4 electron volts, matching the high energy of the near-ultraviolet region of the spectrum. Thin layers of indium, gallium, and nitrogen alloyed in different proportions could be stacked in a solar cell that would span virtually the entire spectrum of sunlight, yielding a solar cell far more efficient than any yet made.

[toadster]

I read about this four years ago and I actually kept the page bookmarked:

Ultra Efficient Solar Cells

Why haven't they actually used this technology? It seems to me that it must not be feasible.

[MrMambo]

An idea I had some years back conserning how to get the maximum amount of electricity out of the sun falling into a particular area.

This consept could possibly convert close to 100% of the solar radiation at a location into electricity.

http://folk.ntnu.no/janerivi/energi/energy.pdf

I know other people have had this idea before. I know that a company back in the 80-ties tried to build something similar. I know nasa build some prototype with fresnel lenses to do about the same thing and got efficiency of over 60%.

The question of course is "How much does it cost?". Does anyone have any idea about people using such approaches today?

[lpetrich]

I note that the "positive charges" are nothing special. They are "holes" or absences of electrons, which act like bubbles in a liquid.

However, what's signfiicant is being able to produce both loose electrons and holes is indium nitride, because one needs a PN junction to make a solar cell work. A PN junction is where a P material (with holes) meets a N material (with extra electrons); such a junction acts as a diode, enforcing one-way electric current flow. The electrons in the N region meet the holes in the P region, making the P region negatively charged and the N region positively charged, thus creating an electric field at that junction.

This induced electric field is what makes a solar cell work; incoming light shakes electrons loose, making an electron-hole pair; the electron moves to the N region and the hole to the P region.

For more, see How Stuff Works.

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But the main problem is that indium and germanium may not be very common materials; though silicon and germanium can both be used in semiconductor electronics, silicon is much more commonly used because it is much more abundant.