September 23, 2019 by Biljana Ognenova
Despite the benefits of solar cells, their manufacturing process involves many expensive and unsustainable practices. The University of Warwick has set a milestone in combating both the harmful chemicals and the costs of solar cell production: enter its new method for patterning copper and silver, based on selective metal vapour condensation—enabled by organofluorine compounds.
Many conventional ways of manufacturing solar panels involve silver and copper. Thanks to its excellent thermal and electrical conductibility, silver has been a preferred metal for solar cells for some time, though it's costly.
Manufacturers have been aiming to reduce the amount of silver in solar cells for years now, and are already far on that track, given that there may be even further reduction in the next decade (to approximately 65 mg per cell).
Still, the price of silver has an impact that must not be undervalued for the mass-scale, versatile production of solar cells, which is looming on the horizon. Copper, its alternative, is cheaper, but it comes with its own set of challenges, which complicates the manufacturing process with additional expensive metals and limits the cell lifetime. Despite these disadvantages, copper seems to be better in terms of overall conversion efficiency.
However, regardless of whether manufacturers choose silver or copper, the problems persist: harmful etching agents during production, plus the cost-effectiveness concerns of the cell manufacturing process, mean that innovative solutions are required.
Left to right: Dr. Ross Hatton, Dr. Silva Varagnolo, and Dr. Jaemin Lee from the Department of Chemistry at the University of Warwick. Image credit: the University of Warwick.
Now, with the non-stick coating method discovery made by the chemistry team at the University of Warwick, including Dr. Ross Hatton, Dr. Silva Varagnolo, and Dr. Jaemin Lee (all pictured above), we could be looking at unconventionally cheaper and greener solar cells that reach the end of the manufacturing process much faster.
In this particular experiment, the old way of patterning and etching metals has been replaced with a new technique similar to the simple thermal evaporation used in making coated crockery. This thermal evaporation is made by a surface coating with an organofluorine compound layer.
Organofluorine is known to have certain pollutant properties, but the extremely thin coating (below 10 nm) produced by the researchers makes it a safe alternative for achieving reduced toxicity.
The chemist team discovered that only a very thin layer of organofluorine compounds does the work, and it prevents silver and copper vapour from condensing on the coated areas—all without leaving metal waste.
The selective deposition of silver on various substrates using a micro-contact printed (perfluorooctyl trichlorosilane) layer. Image credit: Royal Society of Chemistry, Materials Horizons Journal.
Besides being sustainable, this thin layering method is also advantageous in terms of its application versatility. Proven as a low-cost metal deposition method in the packaging industry, it has an extra advantage: shapes and dimensions of the patterned features are only limited by the printing method. For the purposes of the research, micro-contact printing (aka μCP) has been applied, although the researchers state that other printing methods are also possible.
The outcome of the solar cell research showed that fluorinated compound layering is accessible for future advanced sensors, namely those that require uncontaminated metal surfaces for the placement of sensing molecules (for instance, in healthcare).
The fact that the team managed to make a semi-transparent solar cell with a top silver electrode—patterned with a dense array of 2 μm diameter apertures—promises further applications in all areas that require flexible, thin-film solar cells, including construction and EV production.
