Powering wearable technology with flexible, waterproof solar cells

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Researchers at the RIKEN Center for Emergent Matter Science and their collaborators have developed an organic photovoltaic film that is both waterproof and flexible. This allows solar cells to be attached to clothing and function properly even after being exposed to rain or being washed.

One potential application for organic solar power is to create wearable electronics, devices that can be attached to clothing to monitor medical equipment, for example, without the need to change batteries. However, researchers have found that it is difficult to achieve waterproofness without using additional layers, which would reduce the film's flexibility.

Currently published works include nature communications, a group of scientists were able to do just that. They took on the challenge of overcoming a key limitation of previous devices: the difficulty of making them waterproof without reducing flexibility. Photovoltaic films are usually composed of multiple layers. There is an active layer that captures energy at specific wavelengths from sunlight and uses this energy to separate electrons and “electron-holes” into a cathode and an anode. Electrons and holes recombine through a circuit to generate electricity. In previous devices, the hole-transporting layers were typically created sequentially by lamination.

However, in this study, the researchers deposited an anode layer (in this case a silver electrode) directly on top of the active layer, improving the adhesion between the layers. They used a thermal annealing process that exposed the film to air at 85 degrees Celsius for 24 hours. Sixing Xiong, lead author of the paper, said: “It was difficult to form the layers, but we were happy to achieve it, and in the end we were able to create a membrane just 3 micrometers thick. We look forward to seeing the results of the tests.”

What the group got from the test was very encouraging. First, they completely immersed the film in water for four hours and found that it still had 89 percent of its initial performance. He then stretched the film in water 300 times in increments of 30 percent and found that despite the treatment, the film retained 96 percent of its performance. As a final test, I ran it through a washing machine cycle and was able to overcome a challenge that had never been accomplished before.

Kenjiro Fukuda, one of the paper's corresponding authors, said: In the future, we will further develop ultrathin organic solar cells by improving the stability of the devices in other areas such as exposure to air, strong light, and mechanical stress, and make them into practical wearable devices. We plan to make it available for use. ”

In addition to RKEN CEMS, the research group included members from the University of Tokyo and Huazhong University of Science and Technology in China.

reference: Xiong S, Kazuya Fukuda, Kazuya Nakano, et al. Waterproof and ultra-flexible organic solar power generation with improved interfacial adhesion. Nat Commune. 2024;15(1):681. doi: 10.1038/s41467-024-44878-z

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