Dye-sensitized solar cells break a new record

Nov 14, 2011
Green dye-sensitized solar cells © 2011 EPFL

(PhysOrg.com) -- Dye-sensitized Grätzel solar cells have just set a new efficiency benchmark. By changing the composition and color of the cells, an EPFL team has increased their efficiency to more than 12%. Their results have just been published in Science.

A group of scientists in EPFL’s Laboratory of Photonics and Interfaces, under the leadership of EPFL professor Michael Grätzel, has improved the of the famous Grätzel to 12.3%. This performance is now comparable to silicon-based solar panels that are on the market today. And the costs of using this technology have come down slightly. Their results appeared in an article in the November 4 issue of Science magazine.

The challenge was to increase the efficiency of the dye-sensitized cells, in order to produce more electricity. To do this, the chemists replaced the standard dye components – ruthenium and iodine – with porphyrin and cobalt. This combination allows them to increase the absorption of sunlight and results in a more efficient electron exchange. It’s this exchange of electrons from the dye to the substrate that produces electricity.

Grätzel cells mimic the process of plant photosynthesis, and these new dye-sensitized cells take the imitation even closer -- the new chemical combination gives them a greenish tint. This color increases the efficiency of the process that converts light energy into electricity. To get the most out of the light coming from the Sun, the cell absorbs the colors of the spectrum with the highest energies and rejects the rest, which includes the green wavelengths.

Grätzel cells can be used to create flexible, transparent solar panels. They’re a promising alternative for certain applications in which traditional rigid, silicon-based panels cannot be used. In addition, this new efficiency benchmark brings them well within the efficiency range of silicon cells: the theoretical maximum efficiency of Grätzel cells is now 30%, compared with 26% for silicon.

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More information: Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency, Aswani Yella, Hsuan-Wei Lee, Hoi Nok Tsao, Chenyi Yi, Aravind Kumar Chandiran, Md.Khaja Nazeeruddin, Eric Wei-Guang Diau, Chen-Yu Yeh, Shaik M Zakeeruddin, Michael Grätzel, Science, Vol. 334 no. 6056 pp. 629-634, Novembre 4, 2011. DOI: 10.1126/science.1209688

Journal reference: Science search and more info website

Provided by Ecole Polytechnique Federale de Lausanne

4 /5 (12 votes)

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5 / 5 (1) Nov 14, 2011
Eventually we'll have pretty bitchin' artificial trees around.
not rated yet Nov 14, 2011
I'm wondering whether Porphyrin-based Grätzel cells can incorporate the " waffle " design to utilize larger surface area ?


5 / 5 (1) Nov 14, 2011
Fotunately they have quit using Ruthenium-based dyes, since Ruthenium is one of the rarer and most expensive metals on Earth. They are now using Porphyrin (and Cobalt) which is much more common, although fabrication of porphyrin might be an expensive process. I'm surprised that the cost only came down "slightly" when they abandoned Ruthenium.
1 / 5 (1) Nov 14, 2011
dye-synthesized solar cells are still very susceptible to UV radiation aren't they?
4.3 / 5 (4) Nov 14, 2011
Interesting. I'd like to hear how much more efficient or cheap they'd need to be to compete with oil.
4 / 5 (4) Nov 14, 2011
I'd like to hear how much cheaper oil would have to be, once you took away the subsidies and tax breaks and royalty exemptions and state investment in "infrastructure" andother corporate welfare, to compete with solar.
not rated yet Nov 14, 2011
This result is very nice for organic cell, but unfortunately the dye sensitized solar cells aren't very stable. The fact it's not solid state cell - just electrolytic one - is not very advantageous too.
3.5 / 5 (4) Nov 14, 2011
dye-synthesized solar cells are still very susceptible to UV radiation aren't they?

and @rawa:

Correct, that dye sensitized solar cells tend to have shorter lifetimes and are more susceptible to UV damage. Chlorophyll, for example, is also susceptible to damage from UV, even as it harvests the energy. However, plants have regenerative systems that repair or replace the chlorophyll to be used again.

BUT, and this is a big but (and I cannot lie), while many dyes are susceptible to UV, not all of them are. Depending on the exact energy harvesting method, some can take a more catalytic role, without being damaged, while others can take a more active role, and be designed to recombine after it is 'damaged' by the UV.

It gets very complex, but theoretically/mathematically, there should be solutions in the haystack that allow you to have your cake and eat it too.
5 / 5 (1) Nov 14, 2011
dye-synthesized solar cells are still very susceptible to UV radiation aren't they?

So am I. That's why I wear sunscreen.

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