Researchers at the University of Warwick have developed a way to make patterned films of silver and copper for flexible solar cells using cheap organofluorine compounds and without using toxic chemicals. This method is more sustainable and potentially much cheaper because it uses an extremely thin printed layer of organofluorine to prevent metal deposition, so metal is only deposited where it is needed.
The technique is compatible with roll-to-roll mass production. Without using etching or priniting with metal inks, it can be used to make electrodes for flexible solar cells, next generation sensors and low-emissivity glass.
The key to the process is that silver and copper do not condense onto extremely thin films of certain highly fluorinated organic compounds when the metal is deposited by simple thermal evaporation. The researchers showed that the organofluorine layer need only be 10nm thick to be effective, and so only tiny amounts are needed.
This unconventional approach also leaves the metal surface uncontaminated, which Hatton believes will be particularly important for the next generation sensors, which often require uncontaminated patterned films of these metals as platforms onto which sensing molecules can be attached.
The team built thin films with 6 million apertures per square cm and grids of ∼1 μm lines, through to 10 cm diameter apertures. They also built semi-transparent organic flexible solar cells in which the top silver electrode is patterned with a dense array of 2 μm diameter apertures, which cannot be achieved by any other scalable means directly on an organic electronic device.