Researchers at UvA-IoP have shown that certain perovskites possess the desirable property of carrier multiplication – an effect that makes materials more efficient in converting light into electricity.
Research leaders Dr. Chris de Weerd and Dr. Leyre Gomez explain this property, which had so far not been shown to exist in perovskites. When semiconductors – in solar cells, for example – convert the energy of light into electricity, this is usually done one particle at a time: a single infalling photon results in a single excited electron (and the corresponding ‘hole’ where the electron used to be) that can carry an electrical current. However, in certain materials, if the infalling light is energetic enough, further electron-hole pairs can be excited as a result; it is this process that is known as carrier multiplication.
When carrier multiplication occurs, the conversion from light into electricity can become much more efficient. For example, in ordinary solar cells there is a theoretical limit (the so-called Shockley-Queisser limit) on the amount of energy that can be converted in this way: at most a little over 33% of the solar power gets turned into electrical power. In semiconductor nanocrystals that feature the carrier multiplication effect, however, a maximum efficiency of up to 44% is predicted.
This is the main logic behind the search for the carrier multiplication effect in perovskites, and precisely what the UvA-IoP physicists from the Optoelectronic Materials group led by Prof. Tom Gregorkiewicz, in collaboration with the group of Prof. Yasufumi Fujiwara and with support of their colleagues from the AIST National Institute in Tsukuba and the Delft University of Technology have now done. Using spectroscopy methods the researchers showed that perovskite nanocrystals made out of cesium, lead and iodine, do indeed display carrier multiplication. Moreover, they argue that the efficiency of this effect is higher than reported thus far for any other materials; with this finding therefore, the extraordinary properties of perovskites receive a new boost.
Dr. De Weerd says: “Until now, carrier multiplication had not been reported for perovskites. That we have now found it is of great fundamental impact on this upcoming material. For example, this shows that perovskite nanocrystals can be used to construct very efficient photodetectors, and in the future perhaps solar cells.”