Liquid-to-Solid Material Leads to Cheaper, More Environmentally-Friendly Solar Cell
Researchers at Northwestern University have figured out a way to make a solar cell that is inexpensive to make, has a good operating efficiency, doesn't rely on toxic or scarce materials and lasts longer than typical dye-sensitized solar cells.
A previous solar cell design that promised to deliver all of those advantages was the Grätzel cell, a dye-sensitized solar cell that was environmentally friendly and cheap to make. That cell had a major problem though -- the cell's dye-sensitized electrolyte was made with an organic liquid that would leak and corrode the cell, limiting it's lifetime to only 18 months.
The Northwestern team set out to solve the problem of the Grätzel cell. Nanotechnology expert Robert P. H. Chang and chemist Mercouri Kanatzidis put their minds and respective expertise together to craft the new cell. The first part of the solution was a new electrolyte material -- a thin-film compound made up of cesium, tin and iodine, called CsSnI3 -- that starts as a liquid but ends up as a solid. The resulting solid-state cell is inherently stable. The second part was lots of nanotechnology.
“Our inexpensive solar cell uses nanotechnology to the hilt,” Chang said. “We have millions and millions of nanoparticles, which gives us a huge effective surface area, and we coat all the particles with light-absorbing dye.”
Northwestern University describes the make-up of the solar cell like this:
A single solar cell measures half a centimeter by half a centimeter and about 10 microns thick. The dye-coated nanoparticles are packed in, and Kanatzidis’ new material, which starts as a liquid, is poured in, flowing around the nanoparticles. Much like paint, the solvent evaporates, and a solid mass results. The sunlight-absorbing dye, where photons are converted into electricity, lies right between the two semiconductors.
The cell was able to achieve a conversion efficiency of 10.2 percent, the highest so far reported for a solid-state solar cell equipped with a dye sensitizer. This value is close to the highest reported performance for a Grätzel cell, approximately 11 to 12 percent, while 10 percent is usually considered the amount needed for commercialization.
Chang says that the concept is applicable to many different solar cells and the lightweight thin-film structures are also compatible with automated manufacturing. The next step for the team is to build a large solar array with the cells. Their findings were just published in the journal Nature.