Invisible, washable textile embedded solar cells for wearables

Fashion contributes significantly to climate change, accounting for 4% of global carbon emissions. However, our garments may be modified in the near future to actively lower our carbon footprint.

Aalto University in Finland is attempting to make this vision a reality. They devised a way of adhering invisible solar cells to textiles that provide an energy source for wearable electronics such as sensors that assess humidity or temperature during the three-year Sun-powered Textiles project. This would enable designers to build solar-powered clothes without compromising the look of the garment. In addition, the researchers took steps to make solar-cell-infused materials recyclable.

To make a solar cell component machine washable, researchers laminated it between fabrics in a water-tight polyurethane layer. The fabrics containing the solar cell component were then washed dozens of times at 40 degrees Celsius, with the output of the solar cells being monitored after each round in the washing machine. Five of the eight samples preserved their efficiency, while three lost around 20% of their power. Neither the cells nor the fabrics were harmed in the process.

“Now that the solar cell laminated between textiles has been proved to be machine-washable, we have to protect the rest of the components. Our idea is that all of the electric components of the smart textile could be in the same container with the solar cell. That would give us a machine-washable electronic device that’s embedded in textiles and never needs to have its battery charged or replaced,” explains Janne Halme, a university lecturer in the Department of Applied Physics.

The ultrathin solar cell that clings to the textile must have a much bigger surface area than a cell that is placed on top. A piece of ordinary fabric consumes around 70% of a cell's capacity; a more porous fabric consumes a smaller amount.

The material, transparency, crosscut of the fiber, structure of the threads, thickness and weave of the fabric, colors, and finish are all important aspects in the capacity of textiles to let light through. Although light colors transmit light better than dark ones, a fully black and impenetrable fabric can also be used.

Researchers employed commercial silicon solar cells that were made out of a single crystal. They can detect light that is invisible to the naked eye, which is essentially all sunlight. The solar panel, which was wrapped in a layer of fabric, was designed to be exceedingly thin and flexible. Of course, concealing the material consumes some solar energy but increases its endurance by shielding it from the elements.

The material was made up of only one fiber and was designed to be recycled as much as possible. By applying heat to the fabric and then pulling it away, electronic components can be easily removed.

Work apparel, according to the research team, is the most promising application for solar cell textiles right now. Because they are thicker than conventional clothing, the cells have a limited impact on the appearance and feel of the garment. “Curtains are another great way to collect solar energy. They could detect the amount of light and adjust themselves accordingly,” says Elina Ilén, project specialist at Aalto University's Design Department.

“Solar cells hidden under textiles are worth considering as energy sources for electrical equipment that, for one reason or another, has to adhere to textiles, look and feel like a fabric, be machine-washable, use as little power as possible, and whose battery is otherwise either too hard or too expensive to charge or replace,” Halme says.

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