United States national renewable energy Laboratory (NREL) announced confirmed on solar cells will have multiple Exciton generation (MEG:multiple Exciton generation) messages. In PbSe quantum dot solar cells, with the number of electrons and is drawn from the electrode absorbed photon number defined by the ratio of external quantum efficiency per cent ± 114. More content has been see on December 16, 2011 academic journal published scientific papers. For the development of "third generation" solar cell technology, is an important step.
Up to now, conventional solar cells in the photoelectric conversion, relative to 1 be absorbed photon can only produce 1 electron hole pairs (excitons). Maximum power is available from 1 Exciton depends on the band gap semiconductor material. Therefore, the photon energy is less than the band gap of less effects on the photoelectric conversion, and far greater than the band gap of Photonic energy even absorbed by the semiconductor, and can only be obtained with the corresponding power bandgap. Other energy into heat loss. This is known as "Shockley-Queisser limit" is one of the reasons to increase solar cell conversion efficiency.
MEG refers to when the energy band gap twice times when more than 1 photon absorbed by the material, will have two or more phenomena of Exciton. If it can be applied to solar cells, you can break through the limits of high conversion efficiency. If for some wavelengths of light, the internal quantum efficiency of solar cells of 100% or more, you can prove that MEG had happened.
This time, Arthur j NREL researchers. Nozik's team, preparation for energy are 3.44eV UV, quantum efficiency of about per cent, external quantum efficiency of about 130% quantum dot solar cells. Thus confirmed that MEG can occur in solar cells and can be used effectively. Nozik was first predicted in 1997 MEG phenomenon can occur in the semiconductor, and has been leading a MEG study (site reports). Papers wrote that past research has found that internal quantum efficiency for solar cells more than 100%, but access to e-topics, so external quantum efficiency is still low. This not only internal quantum efficiency, external quantum efficiency of solar cells are significantly more than 100%, "this was the decisive evidence suggests that MEG" (thesis).
Confirmed MEG quantum dot solar cells, was in turn on a glass substrate of cascade as a transparent electrode ITO, ZnO 40~60nm thick layers and 50~250nm thickness and Au electrodes made of PbSe quantum dot layer. PbSe quantum dots are produced in a chemical solution. The quantum efficiency of 130%, is a band gap of solar cells is 0.72eV, and energy is 3.44eV (wavelength approximately 360nm) UV region of the ratio of photons. It was alleged that can calculate, MEG is about 2.6 times times the bandgap, or about 1.9eV above (wavelengths around 653nm) of visible light can also occur.
