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Researchers invent printable solar cells for wearable tech

Researchers in Saudi Arabia have developed thin, organic solar cells that can be sprayed via a high-speed printing process onto surfaces. The cells also don’t contain indium – a toxic and increasingly rare metal that’s often used in solar cells.

Because they are fully printable onto surfaces the team says the solar cells could be used to power small sensors, wearable electronics, and other low-energy devices. They’re so lightweight the team was able to rest them on the surface of soap bubbles.

The electrodes are made of a transparent conductive polymer called PEDOT:PSS, with a layer of organic photovoltaic material in the middle. On the outside is a layer of parylene, a waterproof coating that helps seal the electronics against the weather.

“We formulated functional inks for each layer of the solar cell architecture,” said report author Daniel Corzo.

 “Inkjet printing is a science on its own,” he says. “The intermolecular forces within the cartridge and the ink need to be overcome to eject very fine droplets from the very small nozzle. Solvents also play an important role once the ink is deposited because the drying behaviour affects the film quality.”

In tests on glass plates, the team found that the new printed solar cells achieved a power conversion efficiency of 4.73%. That’s not very high in the wider world of solar cells, but the team says it beats the previous record for a fully-printed cell of 4.1%. It also outperforms other types of ultrathin solar cells. When printed onto a flexible substrate, that efficiency went down to 3.6%.

The team says the inkjet printing technique makes them more scalable than other ultrathin solar cells, which are usually made using techniques like spin-coating or thermal evaporation. In 2016, MIT scientists created the thinnest and lightest solar cells ever made – just one-fiftieth the thickness of a human hair and capable of producing up to 6 watts of power per gram.

“The tremendous developments in electronic skin for robots, sensors for flying devices and biosensors to detect illness are all limited in terms of energy sources,” said report author Eloïse Bihar. “Rather than bulky batteries or a connection to an electrical grid, we thought of using lightweight, ultrathin organic solar cells to harvest energy from light, whether indoors or outdoors.”

The research was published in the journal Advanced Material Technologies.

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