Clear, conductive coating could protect solar cells, touchscreens
In today’s touchscreens, the most widely used transparent conductor is ITO but the material is quite brittle and can crack after a period of use. So researchers all around the world are looking for more flexible metal or organic alternatives, but so far, the proposed films were either less transparent or less conductive than ITO, or more costly (when using silver nanowires).
In a study published in Science Advances under the title “Tuning, optimization, and perovskite solar cell device integration of ultrathin poly(3,4-ethylene dioxythiophene) films via a single-step all-dry process”, the researchers improved a flexible version of a transparent, conductive material they had designed two years ago, improving on its optical transparency and electrical conductivity.
The combined transparency and conductivity is measured in units of Siemens per centimeter. ITO ranges from 6,000 to 10,000. Although the new material was measured at 3,000, it is more flexible and could be applied directly to a large-scale, roll-to-roll industrial scale manufacturing process.
The organic polymer is deposited in an ultrathin layer just a few nanometers thick, using a process called oxidative chemical vapor deposition (oCVD), whereby the structure of the tiny crystals that form the polymer are all perfectly aligned horizontally, giving the material its high conductivity. Additionally, the oCVD method can decrease the stacking distance between polymer chains within the crystallites, which also enhances electrical conductivity.
As a demonstration of the material’s capabilities, the team incorporated a layer of the highly aligned PEDOT into a perovskite-based solar cell. With the new oCVD aligned PEDOT, the perovskite’s efficiency improved and its stability doubled.
What’s more, the oCVD PEDOT coating only requires a mild, single-step process at just 140ºC, enabling direct deposition onto plastic substrates such as those use for flexible solar cells and displays. In contrast, the aggressive growth conditions of many other transparent conductive materials require an initial deposition on a different, more robust substrate, followed by complex processes to lift off the layer and transfer it to plastic.
Because the material is made by a dry vapor deposition process, the thin layers produced can follow even the finest contours of a surface, coating them all evenly, which could be useful in some applications. For example, it could be coated onto fabric and cover each fibre but still allow the fabric to breathe, the researchers note.
MIT – www.mit.edu
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