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Organic solar cells harvest indoor light to power IoT devices

Image credit: Linköping University

Organic solar cells that can harvest energy from ambient indoor lights have been developed by researchers in Sweden and China.

While the cells may only be capable of producing small amounts of power, it should be enough to feed many IoT (internet of things) devices that have low requirements.

IoT devices are expected to proliferate in the coming years; many will be sensors that detect and measure moisture, particle concentrations, temperature and other parameters.

The demand for small and cheap sources of renewable energy is increasing rapidly so that the devices can be powered without the need for frequent and expensive battery replacements.

Organic solar cells are flexible, cheap to manufacture and their light-absorbing layer consists of a mixture of donor and acceptor materials. This gives considerable flexibility in tuning the solar cells so that they are optimised for different spectra - for light of different wavelengths.

Researchers in Beijing, China, led by Jianhui Hou, and Linköping, Sweden, led by Feng Gao, have developed a new combination of donor and acceptor materials, with a carefully determined composition, to be used as the active layer in an organic solar cell.

The combination absorbs exactly the wavelengths of light that surround us in typical indoor environments such as living rooms, the library and in the supermarket.

Two variants of the solar cell were developed, one with an area of 1cm2 and the other 4cm2. The smaller solar cell was exposed to ambient light at an intensity of 1000 lux, and the researchers observed that as much as 26.1 per cent of the energy of the light was converted to electricity.

The organic solar cell delivered a high voltage of above 1V for more than 1000 hours in ambient light that varied between 200 and 1000 lux. The larger solar cell still maintained an energy efficiency of 23 per cent.

“This work indicates great promise for organic solar cells to be widely used in our daily life for powering the internet of things”, said Feng Gao, senior lecturer at Linköping University.

“We are confident that the efficiency of organic solar cells will be further improved for ambient light applications in coming years, because there is still a large room for optimisation of the materials used in this work”, said Jianhui Hou, a professor at the Chinese Academy of Sciences.

Last year researchers found that waking up IoT devices using inaudible ultrasound patterns could greatly improve standby battery life.

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