Researchers at the RIKEN Center for Emergent Matter Science and their collaborators have created a flexible, waterproof organic photovoltaic film. This innovative film allows solar cells to be integrated into clothing, maintaining functionality even after exposure to rain or wash cycles.

One potential application of organic photovoltaics is the creation of wearable electronics (e.g., devices that can be attached to clothing that can control medical devices without requiring battery replacement). However, researchers found that waterproofing was difficult to achieve without the use of additional layers that reduce the film’s flexibility.

Breakthrough in photovoltaic technologies

In the study now published Nature Communication, a group of scientists were able to do just that. They set out to overcome the main limitation of previous devices; It is difficult to make them waterproof without sacrificing flexibility. Photoelectric films usually consist of several layers. There is an active system that captures the energy of a specific wavelength of sunlight and uses that energy to separate electrons and “electron holes” into a cathode and an anode. The electrons and holes can then reconnect through the circuit, producing electricity. In previous devices, the electron-hole transport layer was usually created sequentially by layering.

However, for the current study, the researchers placed an anode layer, in this case a silver electrode, directly on top of the active layers, providing better adhesion between the layers. They used a thermal annealing process that exposed the film to air at 85 degrees Celsius for 24 hours. According to the paper’s first author, Xixing Xiong, “forming the layer was difficult, but we were happy to do it, and in the end we were able to create a film that was only 3 micrometers thick, and that’s what we were looking for. I’m waiting for the test results.”

What the group saw during testing was very encouraging. They first completely submerged the film in water for four hours and found that it still retained 89 percent of its original performance. They then stretched the film 30 percent underwater 300 times and found that it retained 96 percent of its performance despite this punishment. As a final test, they ran it through the washing machine and it survived the test, something that had never been done before.

According to Kenjiro Fukuda, one of the corresponding authors of the paper, “What we have created is a method that can be used more generally. “Looking ahead, we plan to continue developing our ultrathin organic solar cells by improving device stability in other areas, such as exposure to air, strong light and mechanical stress, so that they can be used as truly practical wearable devices.”