Researchers Produce Best-Yet Dye-Based Solar Cells

Jul 31, 2008 By Laura Mgrdichian feature

In work that may help solar panels become a more viable source of mainstream power, a research group has created a dye-based solar cell with a high efficiency and high stability, and that lacks the volatile chemicals used in similar cells. This is a combination so far lacking in the newest solar-cell prototypes.

The group, including researchers from the Changchun Institute of Applied Chemistry at the Chinese Academy of Sciences (CAS) and the Swiss Federal Institute of Technology, was studying a new type of solar cell that is being widely researched across the globe, one made of bendy, low-cost, lightweight organic materials rather than rigid, pricey, and often heavy inorganic materials.

"We have uncovered new findings on old solar-cell materials and created high-performance cells," said Peng Wang, a researcher in the Changchun Institute of Applied Chemistry and the study's corresponding scientist, to PhysOrg.com.

The type of organic solar cell Wang and his colleagues improved contains three key parts. The first two components are a semiconductor, such as silicon, and an electrolytic liquid—a conducting solution commonly formed by dissolving a salt in a solvent liquid, such as water. The semiconductor and electrolyte work in tandem to split the closely-bound electron-hole pairs produced when sunlight hits the cell, called excitons (holes are positively charged electron vacancies).

The third component is the source of these photo-induced charge carriers, a photosensitive dye that gives the solar cells their name: "dye-sensitized," with the most common dye being iodide. In addition, a nanomaterial is also often used to hold the dye molecules in place like a scaffold.

The highest efficiency solar cell ever made is dye-sensitized, with an efficiency of 11 percent, meaning 11 percent of the solar energy is converted to electrical energy (compared to 8.2 percent achieved by Wang and his group).

But the highest efficiency dye-sensitized cells also contain volatile solvents in their electrolytes that can permeate across plastic (i.e. organic compounds) and also present problems for sealing the cells. Cells that contain these solvents are therefore unattractive for outdoor use due to potential environmental hazards. So while they perform well, they have serious drawbacks.

Researchers have developed solar cells that use solvent-free electrolytes, but the cell efficiencies are too low.

The cell developed by Wang and his group avoids these issues using a "formulation" they developed. To create their electrolyte, they took three solid salts and mixed them to form a "fascinating" liquid, says Wang. The resulting electrolyte has an impressive conductivity as well as the favorable stability properties of all three salts.

"The performance of our solar cell now matches that of cells that use volatile solvents," said Wang. "This is an important step toward the production of large-scale outdoor dye-sensitized solar cells."

Citation: Yu Bai, Yiming Cao, Jing Zhang, Mingkui Wang, Renzhi Li, Peng Wang, Shaik M. Zakeeruddin and Michael Grätzel 29 June 2008 Nature advance online publication, DOI:10.1038/nmat2224

Copyright 2008 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

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Lord_jag
3 / 5 (5) Jul 31, 2008
8% or 11%? That's pretty bad. Many people on here are citing 30-40%
SLam_to
4.8 / 5 (4) Jul 31, 2008
"The highest efficiency solar cell ever made is dye-sensitized, with an efficiency of 11 percent"

I think they probably ment highest efficiency dye-sensitized solar cell. So far the record is a triple-junction cell at just shy of 41%.
mrlewish
4.6 / 5 (5) Jul 31, 2008
yes and the triple junctions and similar types of cells would cost and arm and a leg to install on a house. Cost per watt is what is important not watts per square meter.
lengould100
3 / 5 (5) Jul 31, 2008
Research all you want (Optical Rectenna design has greater potential than even multi-junction, and the physics has been well-known for years.) The key to actually getting any of this stuff into volume production, thus lowering its cost-per-watt to compete head-on with coal and gas, is to get everyone to start ignoring all the counter-PR being put out by the fossil fuel industries. Witness:

1) Wind generation is likely the least useful and effective, and most costly per-unit-useful-energy renewable available today.

2) A region with a large proportion of wind generation will need to also construct and pay for equivalent amounts of N Gas peaker / standby generation to provide for those hot mid-summer days when peak loads occur and the wind isn't blowing. Large efficient baseload plants have economic difficulty turning on and off to suit the whims of wind generation and so are replaced with very inefficient simple-cycle gas turbines, effectively resulting is worse emissions than if the wind was never built and the gas was burned in a more efficient baseload plant.

3) Because wind is intermittent, the costs of transmission (prices of which are based on $/peak KW capacity, not average) for long-hauling wind generation are 3 to 4x as much PER kwh delivered, as for transmission of power from a useful baseload plant.

4) Because wind generation is very capital-intensive (eg. all it's costs come from costs of equipment for generation and transmission, not fuel), it competes for capital with more useful systems such as Solar Thermal, Biomass, Geothermal, Nuclear and even CCGT-Sequestration coal.

Promoting building wind generation makes so much sense for the Nat. Gas industry and Mr. Pickens (who owns a lot of N Gas) that they must be doing most of the promotion I would guess, though Mr. Pickens must think we are a very stupid lot to be doing it so publicly.
SLam_to
not rated yet Jul 31, 2008
mrlewish, I absolutely agree with you. The triple-junction cells are extreamly expensive per watt, but the article emphasized efficiency and mentions nothing about cost per watt.
NeilFarbstein
not rated yet Jul 31, 2008
what's an optical rectenna, have they been built?
ryuuguu
not rated yet Jul 31, 2008
here is a link 2002 paper on optical rectenna
http://www.nrel.g...3263.pdf
I don't know what has happend since then.
Soylent
5 / 5 (1) Aug 02, 2008
yes and the triple junctions and similar types of cells would cost and arm and a leg to install on a house. Cost per watt is what is important not watts per square meter.


Efficiency does matter.

If you had 3% efficient solar cells that are essentially free it would be a costly proposition to install them simply because of the amount of labour involved.

A year-round average solar insolation of 200W is about the best you can hope for in central Europe. If you wanted to produce 1 KW baseload from 3% efficient solar cells with 50% efficient storage you'd need about 250 square meters of roof to put it on and that's a problem.