Avalanche Effect Demonstrated In Solar Cells

esocid writes "Researchers at TU Delft (Netherlands) and the FOM (Foundation for Fundamental Research on Matter) have found irrefutable proof that the so-called avalanche effect by electrons occurs in specific semiconducting crystals of nanometer dimensions. This physical effect could pave the way for cheap, high-output solar cells. Solar cells currently have relatively low output, typically 15%, and high manufacturing costs. One possible improvement could derive from a new type of solar cell made of semiconducting nanocrystals and could theoretically lead to a maximum output of 44%, with the added benefit of reducing manufacturing costs. In conventional solar cells, one photon can release precisely one electron. However, in some semiconducting nanocrystals, one photon can release two or three electrons, hence the term 'avalanche effect.' This effect was first measured by researchers at the Los Alamos National Laboratories in 2004, and since then the scientific world had raised doubts about the value of these measurements. This current research does in fact demonstrate that the avalanche effect can occur."

Comments

Thermaldynamics?

[mlts]

Without violating thermaldynamic laws, I wonder how much electricity output this will add. I don't think it would double the current flow with 2-3 electrons popping out for each photon that strikes the array, but I know this should add a significant amount of efficiency.

I just hope all these advances, especially ones that make solar cells cheaper to manufacture go into production. There are huge chunks of the world that are lifeless desert, and would be perfect for large solar and wind arrays, assuming one could find a way to transport the generated electricity to cities without too much current loss. Perhaps some chemical reaction that pulls carbon from the air directly to make ethane, then another reaction that converts the ethane to ethanol to be piped to places that can burn the ethanol for electricity. Yes, the chemical reactions to pull carbon from the air, and get it into ethanol are wasteful, but for very long distance transfer of energy (100-200+ miles), it would be less wasteful to do that, than to use standard power transmission lines. Even though the ethanol electricity generating plants would be adding carbon into the air, it would be carbon neutral due to the carbon being extracted at the solar/wind site.

Re:Thermaldynamics?

[Yetihehe]

Perhaps some chemical reaction that pulls carbon from the air directly to make ethane, then another reaction that converts the ethane to ethanol to be piped to places that can burn the ethanol for electricity.

Would methane be ok? If so, it is already done with CO2 and sunlight.

Developing nations

[William Robinson]

This is great news, especially for developing nations whose energy demands are on rising trend. Countries like Indonesia, India and other middle east countries, where sun light is available in abundance, will benefit most.

Re:Isn't price the key?

[syphax]

Efficiency matters, for a few reasons, including:

1. Indirect costs (installation labor, racks, mounts, etc.) scale with the area of the array. The area of array required for a given power output goes with the inverse of efficiency. These costs are pretty significant, so efficiency has a direct impact on installed costs.

2. There's lots of area available for solar panels, but solar energy is pretty diffuse, so you need a lot of area anyway. If a 1% efficient system cost a dime per watt installed, great, but you'd have to cover huge areas to generate significant amounts of electricity. There are practical limits. Even at 10-20% efficiency, you're still looking at large areas to generate a meaningful amount of juice.

Re:Manufacturing Energy Costs?

[syphax]

The numbers are all over the place and constantly coming down with new technologies, but you're looking at breakeven after 1-5 years or so.

This is pretty good (EROEI is >> 1), and will continue to get better.

Re:Sunlight is better used for heating

[TubeSteak]

Using sunlight for electricity is not particularly attractive, but for the neat 'no moving parts' aspect. It is far better to use solar power for light, water and space heating - those remarkable innovations called windows and skylights for example. Tell that to the entire African Continent which has an abundance of sun & empty space, but a deficit of fresh water, power & air conditioning.

I look forward to a future with solar powered desalination plants.
It's a much brighter outlook than continent wide water wars forcefully giving everyone a skylight.

Re:Isn't price the key?

[somersault]

Well, the company I work for is building a 1MW tidal turbine that is around 25 metres tall, not sure exactly how large the vent is, but to me that says that solar energy is pretty diffuse compared to the tides. Sunlight isn't that predictable during the day either unless you can get rid of all the clouds?

Re:APDs

[bperkins]

It's hard to say without seeing the article in Nano-letters, but based on the diagram and a vague description, I'd guess that it works something like this:

A high energy electron hole pair is created by a photon, which then relaxes down to a lower energy state. But, instead of emitting a phonon (heat), it creates another electron hole pair, and you end up with two. I suppose this process could repeat itself, so that many different wavelengths would all produce energy with reasonable efficiency.

This is in all likelihood facilitated by the complex energy band structure of the (essentially) polycrystalline semiconductor.

I'm not so sure how directly applicable all of this is. I suspect that some theorist postulated that this could happen, but it was difficult to prove experimentally. It seems to me that the hard work of actually producing an workable device hasn't been done yet.

From what I can tell, this work is done in PbSe, which I don't think is a suitible for huge volume production.

But I could be wrong in all this.