Scientists in Japan and Germany have devised a simple method to fabricate polymer-based solar cells that can efficiently convert sunlight into electricity.
AsianScientist (Feb. 5, 2018) – A team of researchers at Osaka University in Japan, in collaboration with the Max Planck Institute for Polymer Research in Germany, have invented a polymer that is easy to manufacture and has excellent conversion efficiency of solar power to electricity. They published their findings in Advanced Energy Materials. Humankind is in the midst of a massive drive to harness solar energy to power our homes, gadgets and industries. Plastic solar cells, based on blends of conducting organic polymers, are of interest for making lightweight and cheap solar cells. However, the power efficiencies of these solar cells are very closely related to the way the different types of materials mix and crystallize in thin films. This means complex and careful processing is usually needed to make efficient polymer solar cells. In the present study, a team of scientists led by Assistant Professor Yutaka Ie of Osaka University has devised a polymer that is simple to fabricate but has excellent power conversion efficiency. When light energy excites electrons in a polymer, the excited electrons are transferred to a soccer ball-shaped fullerene and move to the positive side of the solar cell. The space left by an electron is known as a hole, and this hole must also move through the polymer to the positive side of the device to complete the circuit. The researchers thus included a 3-hexylthiophene (HT) spacer unit in their polymer, designed to enhance transport of holes between the two sides of the solar cell. This improved the polymer’s hole conductivity, which in turn enhanced its solar power conversion efficiency. Moreover, the spacer unit and polymer together formed an amorphous blend, that is, the internal structure of the polymer is not rigid. This removes the need to carefully crystallize the material to ensure performance. “Being able to make these cells without having to pay such close attention to the crystal structure of the polymer films could allow us to mass produce these devices by simple printing methods, which should considerably lower costs of the devices and lead to much wider uptake,” said Professor Yoshio Aso of Osaka University.