At the University of Minnesota, sunbathing is a big deal. After six years of soaking up the rays, a team spearheaded by graduate student William Tisdale has discovered a way to potentially double the energy captured by solar cells - giving cells with up to 66% efficiency a bright outlook.
Current cells typically operate at an efficiency rate of around 30%, and a large reason for this is energy loss to due what are known as "hot" electrons. The uppermost layer of a solar cell - the part where the sun hits - is made up of a crystalline semiconductor that is able to able absorb and store the energy shone down upon them. The most common semiconductor in use is silicon, but it tends to get a little bit hot under the collar. As the sun's rays strike the silicon, excess energy is absorbed and transferred into its electrons, which then bleed off the energy as heat.
The Solar Cell Flow: Energy FTW
The problem, as the U of M researches saw it, was twofold. First, although it was impossible to prevent this claiming of excess energy and dispersion as heat, it needed to be slowed down. Second, there needed to be a way to utilize this heat, and the most obvious way was to channel it into a wire or electric circuit in order to harness it before it simply burned off.
Until the U of M got its sunglasses on and beach towels out, all attempts at slowing and capturing these hot electrons had been a wash. Instead of trying to speed up the capture process or make a more efficient wire, the U of M'ers instead looked at using a different crystalline substance to initially absorb the sun's energy.
Enter the quantum dot. These semiconductors are each only a few nanometers wide, and are made of selenide instead of silicon. As a result of their size and material of origin, they lose their hot electrons at a much slower rate than the traditional silicon model. By then introducing titanium dioxide, an inexpensive semiconductor that operates as a wire, the team was able to pull the hot electrons away from the quantum dots before the heat had a chance to dissipate.
Tisdale and his colleagues were quick to point out that this isn't a perfect solution - electrons in titanium dioxide will still lose their "hotness", but the first step has been taken. New panels using quantum dot top layers backed by titanium dioxide semiconductors and flanked by an as-yet unknown third step should, in theory, be able to increase the efficiency of solar cells to 66%, making them a far more viable energy source.
One member of the team, professor Eray Aydil, was confident enough in this new breakthrough to say that "electricity from solar cells is going to be a large fraction of our energy supply in the future". If a scientist says it, it must be true!
Soon enough, we'll be workin' on sunshine. Whoa oh oh.
Source: University of Minnesota