Polymer solar cells are the manufacturers’ and the solar industry’s dream, because they’re easy to make (print), and they’re cheap. Furthermore, they don’t use precious resources like silicon, whose production is energy intensive.
A CA-based company, Solarmer Energy, is now collaborating with professor Luping Yu, from the University of Chicago, to build the best cheapest flexible polymer solar cell ever, one that will be able to reach 10 percent efficiency. It is estimated that if cheap solar cells like Solarmer’s enter the market, they will be able to compete with more expensive silicon and thin film cells, even if they have are a little less efficient.
Yang’s stack of multiple cells that can absorb different bands of light can theoretically harvest 12 to 15 percent of the light’s energy, made entirely from printable polymers. Michael McGehee, a materials science and engineering professor at Stanford University, says: “We still don’t understand the physics well enough to know what the theoretical limit is. I think cells with 15 to 20 percent could be possible.”
Solarmer‘s projected solar cells are made of a semiconducting polymer (the actual solar cell, absorbing photons and releasing electrons), and a carbon nanostructure that sends the converted electrons into the external circuit.
Inside the polymer, electrons go from a low to a high energy level when bombarded by photons. The smaller the difference (or bandgap) between these levels, the more light a cell absorbs, and the higher its efficiency. One way to decrease the bandgap is to bring down the higher energy level. University of Chicago chemistry professor Yu is using this technique to design new types of narrow-bandgap polymers. “The beauty of organic solar cells is that we’re able to engineer new materials that can tailor those energy levels,” Yang says.
The researchers are also trying to improve the interface between the polymer and the carbon nanostructure so that electrons can move faster to the external circuit without getting trapped in the material. And they are developing better electrode materials and improved ways of fabricating the electrodes. Yang says these advances will eventually make it possible to boost the efficiency of individual cells and of stacked cells.
Even if the cells projected by Solarmer and Yang are to be made possible this year, they only predict their market entrance in about three years, with only mild chances of covering laptop bags and cellphone back labels at the beginning of 2011, and then awnings and sunshades. The bigger share of the pie is formed by commercial-grade rooftop panels.
Basides getting them to be more efficient, another main strive behind the solar manufacturers’ work is getting their polymer solar panels to last for longer, at least up to five years. Solarmer’s current cells only last for three. Should they be able to do that, then the reduced efficiency compared to silicon and thin film will be counterbalanced by the low price of organic solar cells.