Driving toward more efficient solar cells

July 11, 2016 by Tracey Peake, North Carolina State University
Driving toward more efficient solar cells
Credit: North Carolina State University

For solar energy to become a real power player in the energy game, solar cells need to be both inexpensive to manufacture and efficient in terms of energy they collect. That's why researchers are focusing their efforts on organic solar cells, which use non-fullerene polymers. These organic polymers are less expensive to produce and some of them, according to some new findings from researchers at NC State and the Hong Kong University of Science and Technology, may have comparable efficiency to their fullerene-based brethren.

NC State physicist Kenan Gundogdu was part of an international team that produced organic with fast charge separation and low voltage loss.

Why is this important? Well, first you have to understand how solar cells work. When sunlight hits a solar cell it is absorbed by the materials in the cell. The light excites these materials, creating a particle called an exciton. The exciton gets split into two charges – an electron (negative) and a hole (positive) – at the interface of two different materials (called donor and acceptor), and then the charges travel to electrodes for collection. Collect enough of these charges, and voila! You can keep the lights on.

However, efficiency is a problem. There are numerous reasons for this, but Gundogdu and colleagues were interested in voltage loss caused by something called the . Since electrons and holes are positively and negatively charged, they attract each other. In organic electronic materials the binding of these particles is so strong that some driving force is necessary to split them. Generally that force comes from the difference in electron and hole attraction preferences of the donor and acceptor materials inside the solar cell. For instance, donor materials will attract holes but not electrons, which leads to separation of the charges at the interface.

Traditionally, a fairly high driving force has been necessary to separate the charges in . The higher the driving force, the faster the charge separation, which sounds like a good thing. But there is no free lunch in physics. With faster comes more voltage loss, which means the solar cell loses efficiency.

But in new findings that were published online in Nature Energy, the research team created an organic solar cell with both a low driving force and low voltage loss. The solar cell also operated at 9.5 percent efficiency (for comparison, the best fullerene operate at a bit under 11 percent).

"We are one step closer to realizing inexpensive organic photovoltaic cells with similar performance to traditional commercial solar cells," says Gundogdu. "These findings also improve our understanding of how solar cells work on the molecular level."

Explore further: Ultrafast charge separation

More information: Jing Liu et al. Fast charge separation in a non-fullerene organic solar cell with a small driving force, Nature Energy (2016). DOI: 10.1038/nenergy.2016.89

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betterexists
1 / 5 (8) Jul 11, 2016
WHO SAID Sun Does Not ALWAYS Shine?
Sun shines in the East while West is Asleep & Vice Versa!
JUST STREAM Energy from East To West & Then from West To East.
No-Brainer Solution here!
Eikka
5 / 5 (6) Jul 11, 2016
The irony is that organic solar cells are sensitive to UV light and break down rapidly in sunshine. They need sunscreen, like a layer of titanium oxide, to reduce the exposure which in turn reduces efficiency by absorbing some of the light, the more the thicker the filter is because the transmittance in the passband isn't full 100%.

A typical camera lens UV filter blocks between 5-10% of the light at the blue-green spectrum and of the most energetic photons.

JUST STREAM Energy from East To West & Then from West To East.
No-Brainer Solution here!


Well it is to a no-brainer. Everyone else has to figure out how to do it, who's gonna pay for it, and what to do when it breaks, how to protect it against attacks, how to keep it running and how difficult is it to maintain when parts of the system must cross the Pacific Ocean and the Atlantic in order to always have solar power available.

WillieWard
1.8 / 5 (5) Jul 11, 2016
JUST STREAM Energy from East To West & Then from West To East.
"As the US National Renewables Energy Laboratory concluded, if renewables were to supply 80% of US electricity, the size of the US transmission network would need to
double."
http://thebreakth...s/9.jpeg
"While the climate benefits of renewables are well-known, the environmental detriments of distributed renewables like wind and solar are rarely publicized."
http://thebreakth.../17.jpeg
"And Breakthrough's analysis of popular renewable scenarios uncovered dramatic land use requirements for renewable energy in 2050."
http://thebreakth.../18.jpeg
http://thebreakth....002.jpg
http://thebreakth....003.jpg
http://thebreakth...ance.pdf
humy
4.5 / 5 (8) Jul 12, 2016
"...the environmental detriments of distributed renewables like wind and solar are rarely publicized."

That is because the environmental detriments of distributed renewables are totally insignificant compared to that of the damage done from burning oil and coal and coal mining etc.Its not news worthy.
"And Breakthrough's analysis of popular renewable scenarios uncovered dramatic land use requirements for renewable energy in 2050."

-Which would be nothing compared to the land lost if we let the sea level rise significantly.
And what are the roofs of houses currently used for that would be stopped if we put solar panels on them?
Eikka
4.3 / 5 (8) Jul 12, 2016
And what are the roofs of houses currently used for that would be stopped if we put solar panels on them?


That's a trick question, because it doesn't account for the external cost of feeding the energy into the grid. For large scale deployment, the avoided cost of not installing the panels is often greater than the value of the energy they would provide because of the difficulties in integrating large amounts of intermittent power into the grids.

the environmental detriments of distributed renewables are totally insignificant


Which is like saying a punch in the gut is insignificant compared to a kick in the face. There's massive amounts of pollution going on with REEs and cheap solar panel production, as well as the inability and non-existence of recycling, or manufacturing things like wind turbine components without fossil fuels and other non-renewable resources.
Eikka
4.3 / 5 (8) Jul 12, 2016
For example, the production of concrete for wind turbine foundations produces CO2, because the only economical way to make cement is by burning limestone in gas fueled furnaces, and the only way to "recycle" cement is to break it up into gravel and fill a road bed with it - otherwise it ends up in a landfill.

Should the wind energy itself be used to produce the cement, and all the other components like the steel, glass fiber, the fuel for the mining truck and other running infrastructure, the sheer inefficiency of converting electricity into fuels and chemicals and materials would bump the price of the power up so high nobody could afford it.

Eikka
4.3 / 5 (8) Jul 12, 2016
Basically, the low cost of renewable energy today is thanks to the low cost of fossil fuels.

You put in fossil fuel energy at a fundamental cost around of 1-2 cents per kWh: cheap Chinese or Russian coal, or American shale gas and oil... and you dig up minerals, process chemicals, run machinery with it and get renewable energy out at a cost of 5-10 cents per kWh at the generator output.

Now, try to close that loop to get rid of the fossil fuel input - or as they say in business, "eat your own dog food". Not so easy is it?
antialias_physorg
4.4 / 5 (7) Jul 12, 2016
Which would be nothing compared to the land lost if we let the sea level rise significantly.
And what are the roofs of houses currently used for that would be stopped if we put solar panels on them?

Add to that the fact that solar and wind don't really care what kind of land they're on (or whether they are on land at all...you can just as well put them out at sea...Even on land the footprint of a windfarm is rather tiny). 'Land use' is only an issue if that land would be used for something else, otherwise. A solar panel ist just as good if it is situated in a desert as if you put it on prime farming land.

Biogas/biofuel has an issue with land use. The idea, however, is to use crops grown on land that isn't useful for other types of agriculture.
dustywells
1 / 5 (1) Jul 12, 2016
"Biogas/biofuel has an issue with land use. The idea, however, is to use crops grown on land that isn't useful for other types of agriculture."

... and grown without fossil fuel and without fertilizer that is sourced from fossil fuel feedstock and harvested without fossil fuel and processed without fossil fuel. Otherwise you end up using more fossil fuel to produce and process the biomass than you replace with the biofuel.
dustywells
3 / 5 (2) Jul 13, 2016
"WHO SAID Sun Does Not ALWAYS Shine?"

Someone whose world does not extend beyond his horizon.
dustywells
1 / 5 (1) Jul 13, 2016
You put in fossil fuel energy at a fundamental cost around of 1-2 cents per kWh: cheap Chinese or Russian coal, or American shale gas and oil... and you dig up minerals, process chemicals, run machinery with it and get renewable energy out at a cost of 5-10 cents per kWh at the generator output.

This is a valid argument as long as we assume that we will always have the input cost of 1-2 cents per kWh.

However, at some point we should be able to use the renewable energy sources that we have created to build more of these units.

Now we must ask ourselves why we would want to use 5-10 cent per kWh of clean, renewable energy instead of 1-2 cent per kWh energy that spews tons of toxins and particulate pollution.
rrrander
2.3 / 5 (3) Jul 13, 2016
Now if solar cells were even marginally as close to the energy density of nuclear, gasoline, nat gas, coal, water, etc., they might be worth $0.10. But, all they done is help Europeans coin the term, "energy poverty."
antialias_physorg
4.2 / 5 (5) Jul 13, 2016
But, all they done is help Europeans coin the term, "energy poverty."

Funny, how we in Europe have never heard of that word. (Other than in the context of where it was coined: to describe lack of access to energy in third world countries)

No one in Europe has to go without power just because they are poor. There's a petrcentage of your welfare that is supposed to be used for energy and upkeep of your living space. If energy prices rise above this you can apply to have this covered by the state for you. (Now some people don't use this part of their welfare for paying their power bills - so they get into trouble. But that's no different from anyone else who doesn't pay their bills.)

This is a valid argument as long as we assume that we will always have the input cost of 1-2 cents per kWh.

Are we counting moving entire cities and fighting off immigration waves due to climate change in these "1-2 cent"? For some reason I think not.
gkam
1.7 / 5 (6) Jul 13, 2016
" But, all they done, . . "
-------------------------------------

They "done good" by me. How many do you have? Mine power my house and my car.
Edenlegaia
4 / 5 (1) Jul 17, 2016
Still waiting for cheap and efficient renewable energy, available for many, if not most people.
It will come. But i don't expect to see it in my mailbox tomorrow.

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