Microwaves Can Advance Solar Cell Production, Recycling: Macquarie University

A microwave technology invented at Australia’s Macquarie University has proved that solar cell recycling can be made easier and so do manufacturing of new solar cells.

During the fabrication of solar panels, silicon goes through several high-temperature processes known as annealing. Currently the cells are cooked in an oven.

A paper now published in the US Journal Applied Physics Letters says that a team led by Dr Binesh Puthen Veettil of the School of Engineering, Macquarie University, has shown that heating using microwave radiation more efficient and its saves considerable time and energy.

Because microwave radiation selectively heats silicon, it leads to almost instantaneous effects with massive savings of energy. This is partly because the rest of the laminated panel of glass, plastic and aluminium is left largely unaffected. Macquarie University says that property that has led to an unexpected recycling benefit for which the group has a patent pending.

Recycling Benefits

Under microwave treatment, the plastic (ethylene vinyl acetate) coating that protects the silicon plate from moisture and contamination softens to the point where it can be peeled off mechanically. Macquarie University held that this means the plate can be easily delaminated and its components reused without employing harsh chemicals.

“Until now it made economic sense to just dump the panels in the landfill,” says Dr Binesh Puthen Veettil. “In the rare instances when they are recycled, you crush the panels, heat them to about 1400°C and wash them with chemicals to remove the plastic — a highly energy-demanding process.”

Macquarie University lecturer added that now, as the solar panels which began to be installed in vast numbers about 20-30 years ago are reaching the end of their life and being decommissioned, governments are demanding they be recycled.”

Selective Annealing

Microwave annealing has several other advantages, says Macquarie University paper. The ability to focus microwave radiation means the heating it induces can be selective and highly tuned. Some of the newer panels, for instance, employ what is known as heterojunction technology, where crystalline and amorphous silicon are interleaved. In these cells, faster, better-directed annealing is highly advantageous.

Precise focusing also means that annealing can be directed to specific parts of the solar panel, making it ideal for annealing solar panels with more intricate internal structures fabricated for special purposes.

And, in contrast to an oven where all sorts of chemical substances are shed from the walls, microwave annealing takes place in a clean environment. “So there is less contamination,” says Dr Veettil. “And the whole process can all be undertaken at room temperature.”

There are several other projects involving solar cells and sustainable energy underway at Macquarie. One of the co-authors of the annealing paper, Associate Professor Shujuan Huang, leads a group looking at microwave annealing in perovskite solar cells.

Macquarie University held that Dr Veettil’s research in collaboration with the school of photovoltaics at UNSW, was initiated with funding from the Australian Centre for Advanced Photovoltaics and has been further supported by the Australian Government through the Australian Renewable Energy Agency (ARENA).