Dye-Sensitized Solar Cells Set New Efficiency Benchmark with Low-Volatility and Solvent-Free Electrolyte
29 October 2008
Researchers in China and Switzerland are reporting efficiencies as high as 10% from new practical dye-sensitized solar cells (DSCs, or Grätzel cells) with low volatility and solvent-free electrolyte. In addition to the higher efficiencies, the new cells also showed greater stability at high temperatures than previous formulas, retaining more than 90% of their initial output after 1,000 hours in full sunlight at 60°C. Their study is scheduled for the 13 November issue of ACS’ The Journal of Physical Chemistry C.
The research, conducted by Dr. Peng Wang of the Chinese Academy of Sciences and colleagues—including Dr. Michaël Grätzel, inventor of the first dye-sensitized solar cell—involves photovoltaic cells composed of titanium dioxide and a new type of ruthenium-based dye that helps boost the light-harvesting ability.
DSCs are less expensive than standard silicon-based solar cells and can be made into flexible sheets or coatings. Although promising, DSCs have had serious drawbacks, including low conversion efficiencies, a drop in performance after relatively short exposures to sunlight, and the use of toxic and volatile solvents, which require expensive hermetic sealing.
Using a volatile electrolyte, DSC technology has delivered efficiency of up to 11.0-11.3% measured under the standard air mass 1.5 global (AM 1.5G) sunlight—about half that of the best silicon solar cell. [AM 1.5G is the intensity of insolation equivalent to the sun shining through the atmosphere to sea level, with oxygen and nitrogen absorption, at an oblique angle 48.2 degrees from the vertical (zenith).] Despite the lower efficiencies, the DSCs offer stable output over a moderate temperature range as well a response to weak and diffuse light.
In the past several years, much work has been focused on the development of practical DSCs by using low-volatility electrolytes, solvent-free ionic liquids, or solid organic hole-transporters. Promoted by material designing together with device engineering, the highest efficiency of a stable device with a low-volatility electrolyte now stands at 9.1%, whereas that of its counterpart with a solvent-free electrolyte is 7.7%.Shi et al. (2008)
Using a nanocrystalline titania film stained with the new ruthenium sensitizer, the researchers achieved 9.6-10.0% and 8.5-9.1% efficiencies in conjunction with low-volatility and solvent-free electrolytes under AM 1.5G solar illumination.
The research team is working on stability studies of a testing cell at 80° C and long-term evaluations of a large solar panel with the newly developed systems.
Resources
Dong Shi, Nuttapol Pootrakulchote, Renzhi Li, Jin Guo, Yuan Wang, Shaik M. Zakeeruddin, Michaël Grätzel, and Peng Wang (2008) New Efficiency Records for Stable Dye-Sensitized Solar Cells with Low-Volatility and Ionic Liquid Electrolytes ASAP J. Phys. Chem. C, doi: 10.1021/jp808018h
Yu Bai, Yiming Cao, Jing Zhang, Mingkui Wang, Renzhi Li, Peng Wang, Shaik M. Zakeeruddin and Michaël Grätzel (2008) High-performance dye-sensitized solar cells based on solvent-free electrolytes produced from eutectic melts. Nature Materials 7, 626 - 630 doi: 10.1038/nmat2224
At 60C! Damn! Give ambient heat dissipation a chance.
I wonder if direct exposure to sunlight is the way to go with DSS cells. If the materials are cheap enough I could see a bundled tube approach (imagine literally bundling tiny pipes with the inner wall being a DSSC) being better for conversion efficiencies and life span. This would essentially represent a negative concentration ratio and would turn direct, high intensity sunlight into low incidence low intensity sunlight. Seems counter-intuitive, I know, but sometimes such radical and contrarian approaches pay off.
Posted by: GreenPlease | 29 October 2008 at 08:32 AM
Green,
There was a similar view expressed re uv sensitive plastic photovoltaic that could effectively re coupe energy from indoor and indirect lighting.
Seemed to be saying office furniture or other plastic products can provide much of their potential outputs from artificial and indirect lighting for very little extra cost.
I wonder if the NF3 described in an ealier article is one of the nasty solvents.
Sometimes it seems we can't win a trick with many advances in efficiency bringing a whole new set of issues.
Posted by: arnold | 29 October 2008 at 03:22 PM
Nice but if they need Ruthenium we won't cover the roofs with that stuff, it is even rarer than Platinum (5 times rare in fact) so doesn't look like DSSC will be competitive any time soon.
Posted by: Treehugger | 29 October 2008 at 04:58 PM
I had similar concerns re: Ru. I couldn't help but ask myself "how can this be cheaper than Si when they are using one of the rarest elements on earth?"
Posted by: GreenPlease | 30 October 2008 at 05:36 AM
The current annual world production of ruthenium could be multiplied by a factor of several if commercial nuclear reactor fuel were reprocessed and Ru extracted. More than 6% of the mass of 235U fissioned is converted to ruthenium (rhodium is also produced in some quantity). You'd have to let the fuel cool for several decades to deal with the longest lived Ru radioisotopes, though.
Posted by: Paul F. Dietz | 30 October 2008 at 05:57 AM
I think they can be cheaper because the amount of Ruthenium used in the cell is actually very small. Silicon-based cells are just that - based on silicon, they use silicon as a substrate with different layers doped with trace amounts of other elements. These new cell are actually composed of titanium dioxide which, if I'm reading it right, has been sensitized by a dye. The dye could be a chemical compond made up of cheap elements and only built around a lone Ruthenium atom.
This is how plants do it, the chlorophyll molecule (it's really a family of molecules) can have over 130 atoms in it. Most of these are hydrogen and carbon, a few are oxygen and nitrogen, and one is a magnesium ion.
Posted by: ai_vin | 30 October 2008 at 07:58 AM
In terms of Dye, Ru(bpy)3 is one of many possibilities. There are other organic dyes in the works. As the other reader said, Ru used in the cell is merely one mono layer of material coated on TiO2 surface. The cost is not on the material itself. The overall COO (Cost of Onwership) is at the life time of the cell. Please note, as long as we can make electricity at 10 cent per kWh, we will be in business.
Cheers.
Posted by: Xiaohong Chen | 10 November 2008 at 07:29 AM
haven't the boffins at MIT already done this? Also, Nanosolar are making something similar as well
Posted by: Total Solar Energy | 16 December 2008 at 09:02 AM