Indian Scientists Recover Pure Silicon from Obsolete Solar Cells

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The disposal of used photovoltaic panels is increasing day by day around the world, necessitating the need for an efficient recycling method to decrease environmental pollution. The average life expectancy of solar panel is about 25-30 years. Today, worldwide, around 60 million tons of solar cells, which are in their end-of-life stage, have become wastes.

Indian scientists working at KPR Institute of Engineering and Technology, Tamil Nadu, have devised a way to efficiently recover pure silicon and other materials such as aluminium, silver, and lead from disposed solar cells using chemical treatments.

Earlier, pure silicon was recovered by treating the solar cells with hydrofluoric acid or a mixture of hydrofluoric acid and other chemicals. The KPR scientists eliminated the usage of hydrofluoric acid in their work as the chemical is highly toxic and corrosive. Instead, they recovered pure silicon (99.9984%) by sequentially treating the solar cells with three different chemicals. Aluminium, silver, and lead were also recovered as aluminium hydroxide, silver chloride, and lead oxide, respectively.

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In the course of their research, the scientists treated the solar cells with some specific chemicals and found that the aluminium layer was removed through using concentrated sodium hydroxide solution. The hydrogen formed during the reaction was collected in a chamber to be used later as fuel. The aluminium hydroxide from the sodium hydroxide solution was separated by filtration. Similarly, the silver and lead were removed by treating the solar panel with nitric acid. The released nitrogen dioxide was collected to be used later for the production of nitric acid.

Further, to separate silver nitrate, the solution was treated with hydrochloric acid, resulting in silver chloride being formed. The precipitated silver chloride was then filtered out. The solution was treated with sodium hydroxide to separate lead compound from the solution. The lead oxide was then converted to lead hydroxide, and the precipitated lead hydroxide was filtered.

The antireflecting coating (blue in color) and p-n junction were the only impurities in the process, which were removed using concentrated phosphoric acid. As a result of this long treatment of the solar cell, pure silicon (99.9984%) was obtained.

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As per the scientists’ calculation, the recycling cost for 1 kg solar cell turned out to be $68.9. Therefore, the total profit after recycling 1 kg solar cell was found to be around $185.

Solar recycling has been gaining attention in recent time as a result of rising efforts to combat climate pollution. For instance, as part of the National Recycling Week, the Dubbo Regional Council (DRC), a local government area located in New South Wales, Australia, participated in a first-of-its-kind trial project recycle second hand (serviceable) solar panels, hoping that residents will one day be able to reuse solar panels in their own homes or businesses.