Pseudoparticles Find Crucial Role in Energy Conversion

Pseudoparticles could help make more efficient the conversion of light into storable energy, ushering in the potential for a decisive sustainable energy supply.

Using the photoactive zinc oxide material, the formation and migration of polarons is demonstrated. Courtesy of Patrick Rinke/Aalto University.

A team from the Karlsruhe Institute of Technology (KIT), in collaboration with the Fritz Haber Institute in Berlin and the Aalto University in Helsinki, Finland, has discovered that the formation of polarons (pseudoparticles comprising a particle and its interaction with the environment) in zinc oxide can travel through photoactive material until they are converted into electrical or chemical energy at an interface.

The researchers used a photoactive zinc oxide material, as well as IR reflection–absorption spectroscopy (IRRAS) with a time resolution of 100 ms to examine the formation and migration of polarons.

According to the study, published in Nature Communications (doi: 10.1038/ncomms7901), “polarons represent a crucial intermediate step populated immediately after dissociation of the excitons formed in the primary photoabsorption process.”

“Conversion of photons, i.e., light particles, into electricity takes several steps,” said Christof Wöll, director of the Institute of Functional Interfaces at KIT.

First, light is absorbed in a photoactive material before single electrons are removed from their sites, leaving a hole behind; the resulting electron-hole pairs are only stable for a short time. Such free holes are not stable in most materials, the researchers said, but rather are converted into polarons under energy loss. The photoexcited polarons are stable for a longer term, enabling a potential sustainable conversion process of the pseudoparticles into electrical or chemical energy.

For more information, visit: www.kit.edu.