"The United force of nature, but separated by the force of man" — sounds like a description of a love story, but it is also a basic description of how scientists began to make more efficient organic solar cells. This tells Scientific Portal ScienceDaily.
At the atomic level, organic solar cells function as feuding families of Romeo and Juliet. There is a natural force of attraction between positive and negative charges, which occur when a photon exposure of cells. However, in order to capture the energy that these charges should be separated. When these charges exist in bound form, they are referred to by scientists as the "exciton".
"The real question that this work is trying to answer, is how to create a material that can split exciton with less energy," — said a senior chemist at Argonne National Lin Chen Laboratory of the Ministry of Energy of the United States of America. "Excitons can be considered a kind of" quasi-particles "because they behave in a special way. When two charged exciton region, that is, the electron and the area known as" the hole ", are close to each other, they are difficult to separate. Closer these holes and electronic field in the exciton, the more likely their repeated association without generating electricity. When you add energy to the system, the charges begin to separate, giving the free electrons and holes, and, ultimately, allow current to generate electricity and produce "- explained Chen. "Thus, if the two charged exciton region, which we discussed earlier, will be pre-separated, or polarized, most likely, they will be able to avoid falling into the trap potential and become effective carriers of the charge."
In the process of a new experiment Chen and his colleagues studied how four different molecules in the polymer layer, located in the middle of the solar cell, causing various exciton dynamics. They found that the excitons, which are polarized to a greater extent, are key to the creation of more efficient solar cells based on polymers.
"If the normal exciton immediately after it was formed, has a hole and the electron, which are located in almost the same place, the new materials allow the exciton, which is more polarized at the beginning" — said Chen.
Currently, a joint team is exploring new materials to create high organic solar cells based on these results. In organic solar cells still have the opportunity to become closer in their effectiveness to their inorganic, silicon-based, competitors, as they are more attractive in terms of monetary cost.
"Further study of the electronic dynamics of organic photovoltaics is important to improve the efficiency of organic solar cells and, thus, the creation of solar energy, which will be competitive in terms of cost compared to conventional sources of energy," — concluded Chen.