So small that 250 billion would fit comfortably on the head of a pin, the nanocrystal solar cells recently developed at the University of Southern California point the way toward liquids or inks that could be sprayed, painted or printed on materials to harvest the sun’s rays as electricity via photovoltaics.
In fact, according to Richard L. Brutchey, assistant professor of chemistry at USC’s Dornsife College, who worked with postdoc David H. Webber to create a new surface coating for the nanocrystals made from cadmium selenide, these liquid-suspended nanocrystals–also known as quantum dots–are much cheaper to make than monocrystalline silicon wafer solar cells. The trick in making them viable is in upping their efficiency.
The solution was to find a stable fluid medium that also conducts electricity, and the team did so using a synthetic ligand that not only allowed for a steady and symmetrical deposition within the liquid, but actually generated connections between the nanocrystals to aid electrical transmission. In addition, Brutchey and Webber were able to use a low-temperature process for the doping, which meant future deposition on plastic (again, cheaper than glass) would not cause the surface to melt. And this in turn could lead to low-cost building integrated photovoltaic (BIPV) films for windows and building sheathing or cladding.
While both scientists acknowledge that the technology is years away from commercialization, they also say that they plan to continue research using something other than cadmium for the nanocrystalline solar cells, since cadmium is restricted due to its toxicological profile. This (cadmium selenide) is the same ingredient used in the solar paint we wrote about last year, which in its very early stages of development has an even lower efficiency threshold, at 1 percent.