Is light a conductor of electricity?

Transparent electrical conductors made from correllated metals

Transparent and electrically conductive at the same time: only very few materials meet these requirements. One of the most important is indium tin oxide, which is used in thin layers in displays, solar cells and organic light-emitting diodes. Since the costs - especially for the metal indium - rise with increasing demand, cheaper alternatives are being sought. Scientists have now found what they are looking for in special metal oxide compounds. As they report in the journal Nature Materials, these so-called correlated metals are permeable to visible light and conduct electricity even better than indium tin oxide.

"Transparency requires little absorption and reflection of light particles," explain Roman Engel-Herbert and his colleagues from the American Pennsylvania State University. For electrical conductivity, the concentration of charge carriers such as electrons must also be as high as possible. The scientists saw precisely these two conditions in two metal oxides, strontium vanadate and calcium vanadate. Using epitaxial processes, they produced layers 4 to 45 nanometers thick from these correlated metals and checked their physical properties.

Because of their high concentration of charge carriers, both compounds showed good electrical conductivity of up to 35,000 Siemens per square centimeter. This enabled them to conduct electricity even better than the indium tin oxide, which was often used up to now, with around 10,000 Siemens per square centimeter. Photons in the visible spectral range were only insignificantly swallowed or reflected by both compounds. All material samples produced were therefore transparent. The electronic properties of the two types of crystals were responsible for these properties, with an optimal structure of the valence and conduction bands for electrons for transparency.

Based on these results, which Engel-Herbert and colleagues also supported with a theoretical model, correlated metals could become an economically interesting alternative to expensive indium tin oxide. Further material combinations, in which strontium and calcium are replaced by other metals, could enable even higher charge carrier densities.