Researchers have made plastic conductive while also making it more transparent. The recipe obtains the best balance between conductivity and transparency by creating a three-layer anti-reflection surface. The conductive metal layer is sandwiched between two “dielectric” materials that allow light to pass through easily. The dielectrics reduce the reflection from both the plastic and metal layer between them.
The process creates coatings with high transparency and conductivity, low haze, flexibility, easy fabrication, and compatibility with different surfaces. Previously, the researchers demonstrated that it was possible to add a layer of metal onto a plastic sheet to make it conductive — a very thin layer of silver that, by itself, reduced the transmission of light by roughly 10 percent.
Light transmission through plastic is a little lower than through glass but its transparency can be improved with anti-reflection coatings. The dielectrics chosen are aluminum oxide and zinc oxide. On the side closest to the light source, the aluminum oxide reflects less light back to the source than the plastic surface would. Then comes the metal layer composed of silver with a tiny amount of copper in it, just 6.5 nanometers thick, and then zinc oxide helps guide the light into the plastic surface. Some light still gets reflected back where the plastic meets the air on the opposite side but overall, the light transmission is better than the plastic alone. The transmittance is 88.4 percent, up from 88.1 percent for the plastic alone.
The “recipe” indicates how transparent a dielectric-metal-dielectric conductor could be for a target electrical conductance. The tricks are selecting the right dielectrics and then figuring out the right thickness for each to suppress the reflection of the thin metal. In general, the material between the plastic and metal should have a higher refractive index, while the material nearest the display or light source should have a lower refractive index.
Transparent conductors in solar cells for mounting on windows could absorb infrared light and convert it to electricity while leaving the visible spectrum to brighten the room. The coatings also could be used on large-panel interactive displays and car windshields that can melt ice the way rear window defrosters can.