A network of “electron highways” runs through a crystal in fine lines. It is lead halide perovskite. The material is suitable for producing cost-effective and efficient solar cells.
It was previously unknown why this particular material has such a high conductivity. Now physicists from the Institute of Science and Technology in Austria have found an explanation and in the trade magazine Nature Communications published. Impurities and defects in the crystal are crucial.
When light hits a solar cell, electrons are knocked out of their connections and are therefore free to move. Holes remain at these points, which act like positive charge carriers and can also migrate through the material. In order for the energy of light to be converted into electrical energy, electrons and holes must be separated by an external voltage. The transport of cargo should be as efficient as possible; In addition, electrons and holes must be prevented from recombining.
Most solar cells are currently made of silicon. The high conductivity is achieved through the greatest possible purity in the material. However, this is associated with high manufacturing costs.
Lead halide perovskites, on the other hand, have high efficiency precisely because of impurities. Changes in the crystal structure create internal forces that separate electrons and holes and prevent recombination. This does not occur equally throughout the entire material, but only on so-called domain walls, which run as a network through the entire crystal. Charge carriers move particularly efficiently along these domain walls, like on a highway. By introducing silver ions into the crystal, this network of domain walls could be made visible under the microscope.
Perovskite solar cells are not yet suitable for widespread use, mainly due to their short shelf life. A deeper understanding of how it works can potentially help solve the existing problems and enable easier and cheaper production of solar cells.