The first solar cell with an external quantum efficiency (EQE) that exceeds 100 percent for photons with energies in the solar range has been created. With these new solar cells, every blue photon that is absorbed can generate up to 30 percent more current than with current technologies.
The external quantum efficiency is the measure of how many photons are converted into electrons within a device.
“While traditional semiconductors only produce one electron from each photon, nanometer-sized crystalline materials such as quantum dots avoid this restriction and are being developed as promising photovoltaic materials,” an AVS news release notes. “An increase in the efficiency comes from quantum dots harvesting energy that would otherwise be lost as heat in conventional semiconductors. The amount of heat loss is reduced and the resulting energy is funneled into creating more electrical current.”
The researchers made use of a process named multiple exciton generation (MEG), so that every blue photon that is absorbed can create at least 30 percent more electric current than other technologies currently allow.
Multiple exciton generation works by “efficiently splitting and using a greater portion of the energy in the higher-energy photons.” Doing this, the researchers were able to create an EQE value of 114 percent for 3.5 eV photons. This proves that the concept can be functional in an actual working device.
Joseph Luther, a senior scientist at NREL, believes MEG technology is going in the right direction. “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,” Luther said. (Editor’s note: “too expensive” only if you don’t take into account health or environmental costs of fossil fuels; and, not even taking those into account, solar is cost competitive with other energy options in some regions now.)
“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,” Luther adds.