Demonstration of an electret generator using self-assembled electret for energy harvesting without any charging process

Electret generators (EGs) for energy harvesting is a device which ambient vibrations convert into electric energy. They are expected as power supplies for low energy applications such as wireless sensors. In EGs, charges are induced by an electric field of electret, and thus output power is determined by a surface charge density (sigma) of the electret. Various charging processes were proposed so far to realize the electret with high sigma, however, they were one of problems decreasing productivity. The elimination of the processes is extremely desired. In this study, we developed charged film composed of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl) benzene (TPBi) without any charging process. A surface potential (SP) exceeded 46 V for ca. 740 nm thick film due to spontaneous orientation of TPBi, and was sufficiently stable under room light illumination in atmosphere. Finally, we demonstrated EGs utilizing TPBi as electret generated an AC current of the order of nano-ampere in environmental condition, indicating the feasibility of EGs using TPBi film in practical atmosphere. The series of results strongly suggested that application of spontaneous orientation of polar molecules was promising for the realization of EGs with high productivity.