Recently, scientists at the University of Leicester in the UK have discovered a new method to recover 95% of the metals (silver and aluminum) from end-of-life photovoltaic cells in less than 10 minutes. This method is said to be cheaper and more environmentally friendly than the current recycling method using mineral acids.

The researchers applied the technique to a crystalline silicon solar cell measuring 12 × 15 cm and weighing 2 g, which consisted of a 100-micron-thick silicon wafer coated with a 100-nanometer-thick silicon nitride antireflection layer on the front side. , the backside is coated with a 20-micron-thick aluminum wafer.

The researchers said, "First, we put the solar cell in an aluminum chloride solution. The aluminum electrodes were removed from the silicon wafer. We used ultrasonic waves to promote the dissolution of aluminum, which occurred within minutes. Considering aluminum's Low cost, there may be no economic benefit to recycling aluminium, but aluminium salt solutions can be used for wastewater treatment.”

They further explain, “In the second step, the silver in the solar cells is dissolved in either choline chloride or calcium chloride brine using ferric chloride, which takes about 10 minutes. Found in chicken feed and in gravel used on roads to avoid icing, it is readily available, inexpensive and low toxicity."

“Interestingly, iron dissolved in water cannot oxidize silver, but iron dissolved in brine can. Replacing water with brine improves the iron’s ability to oxidize silver and increases the solubility of silver in brine. This is due to chloride ions in brine. Silver chloride is then precipitated by adding water to the brine to dilute chloride ions. Silver chloride is easily filtered out of solution," he added.

In the end, the process successfully recovered silver chloride with a purity of 98 percent, and according to the researchers, in a further step, silver chloride can be converted into metallic silver, thereby increasing its purity. The process does not affect silicon wafers and nitride anti-reflective coatings, opening up the possibility to reuse silicon wafers in photovoltaic panels or process them for other uses.

However, the above results were obtained in a laboratory setting and may vary on an industrial scale. However, researchers believe that industrialization is feasible because they use chemicals that are cheap, low toxicity, and readily available. The research results have been recently published in the "Journal of Cleaner Production".