Single atomic layers are combined to create novel materials with completely new properties. Layered oxide heterostructures are a new class of materials that has attracted attention among materials scientists in the last few years. A research team at the Vienna University of Technology, together with colleagues from the USA and Germany, has now shown that these heterostructures can be used to create a new kind of extremely efficient ultra-thin solar cells.
“Single atomic layers of different oxides are stacked, creating a material with electronic properties which are vastly different from the properties the individual oxides have on their own,” said Professor Karsten Held from the Institute for Solid State Physics, Vienna University of Technology.
In order to design new materials with exactly the right physical properties, the structures were studied in large-scale computer simulations. As a result of this research, the scientists at TU Vienna discovered that the oxide heterostructures hold potential for building solar cells.
The basic idea behind solar cells is the photoelectric effect. Its simplest version was already explained by Albert Einstein in 1905: when a photon is absorbed, it can cause an electron to leave its place and electric current starts to flow. When an electron is removed, a positively charged region stays behind – a so called ‘hole’. Both the negatively charged electrons as well as the holes contribute to the electrical current.
“If these electrons and holes in the solar cell recombine instead of being transported away, nothing happens and the energy cannot be used,” said Assmann, who carried out a major part of the computer simulations at TU Vienna. “The crucial advantage of the new material is that on a microscopic scale, there is an electric field inside the material, which separates electrons and holes.” This increases the efficiency of the solar cell.
The oxides used to create the material are actually isolators. However, if two appropriate types of isolators are stacked, an