Engineering 101

Cheaper, More Sustainable Patterned Metal Production for Solar Cells and Electronics

By Ruth Seeley

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University of Warwick chemists have developed an innovative way to pattern metals— which could make the next generation of solar panels more sustainable and cheaper—by using cheap organofluorine compounds without toxic chemicals.

The patterned silver and copper films were made using an extremely thin printed layer of organofluorine to prevent metal deposition. That means the metal is only deposited where it is needed. The process can also be used to make electrodes for flexible solar panels, next-generation sensors and low-emissivity glass

Silver and copper are the most widely used electrical conductors in modern electronics and solar cells. However, conventional methods of patterning these metals to make the desired pattern of conducting lines are based on selectively removing metal from a film by etching using harmful chemicals or printing from costly metal inks.

The Warwick patterning process should prove much more sustainable and cheaper for large scale production, because there is no metal waste or use of toxic chemicals, and the fabrication method is compatible with continuous roll-to-roll processing.

The researchers discovered 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.

Thermal evaporation is already widely used on a large scale to make the thin metal film on the inside of potato chip and other snack packages, and organofluorine compounds are already commonplace as the basis of non-stick cooking pans.

The organofluorine layer need only be 10 billionths of a meter 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.

To help address the challenges posed by climate change, there is a need for color-tunable, flexible and lightweight solar cells that can be produced at low cost, particularly for applications where conventional rigid silicon solar cells are unsuitable such as in electric cars and semi-transparent solar cells for buildings.

Solar cells based on thin films of organic, perovskite or nano-crystal semiconductors all have the potential to meet this need, although they all require a low cost, flexible transparent electrode. Hatton and his team have used their method to fabricate semi-transparent organic solar cells in which the top silver electrode is patterned with millions of tiny apertures per square centimeter, which cannot be achieved by any other scalable means directly on top of an organic electronic device.

“This innovation enables us to realize the dream of truly flexible, transparent electrodes matched to needs of the emerging generation of thin-film solar cells, as well as having numerous other potential applications ranging from sensors to low-emissivity glass,” said Dr. Ross Hatton, Department of Chemistry at the University of Warwick.

Source: University of Warwick

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