Conventional solar cells capture photons in sunlight and turn it into electricity. This is also true for solar cells that use quantum dots as the photovoltaic material, but with quantum dots, it`s actually possible to harvest “lost” energy that otherwise would end up as heat. This feature is promising to improve overall conversion efficiency of solar cells, which in turn will reduce costs.
The efficiency for quantum dot solar cells have previously been limited to 5.4% - about four times less than our some of our commercial solar cells based on crystalline silicon semiconductors. Scientists at NREL have now demonstrated the first quantum dot solar cell with external quantum efficiency (EQE) over 100%. In laymen’s terms, this is to say that every photon is capable of “freeing” more than one electron.
As a result, every photon could on average generate 30 percent more electrical current than in conventional solar cells. The scientists were able to unleash a greater potential by utilizing higher-energy photons as well. This is done through a process called multiple exciton generation (MEG), which allows multiple electron-hole pairs to form from the absorption of a single photon.
Joseph Luther, one of the senior scientists at NREL, had the following to say on the new technology:
“Since current solar cell technology is still too expensive to completely compete with non-renewable energy sources, this technology employing MEG demonstrates that the way in which scientists and engineers think about converting solar photons to electricity is constantly changing […] There may be a chance to dramatically increase the efficiency of a module, which could result in solar panels that are much cheaper than non-renewable energy sources.”
There is clearly a lot of potential in quantum dot solar cells. That being said, the technology is still far from ready for the market.
Mathias writes more about new solar technologies and their costs at Energy Informative
Image credit: Wikimedia Commons