Operation Mechanism of Electret-Based Vibrational Energy Harvesters Utilizing Spontaneous Orientation Polarization

Abstract

In recent years, electret-based vibrational energy harvesters (E-VEHs) have attracted attention as autonomous power sources for low-power devices such as sensors. Electrets, which are insulating materials that (quasi-) permanently hold electric charge or polarization, play a crucial role in E-VEHs. However, their fabrication traditionally requires charging of insulating materials using methods like corona discharge, which has been a limiting factor in the productivity of E-VEHs. To address this challenge, we proposed E-VEHs utilizing the spontaneous orientation polarization (SOP) phenomenon. Thin films of materials such as tris- (8-hydroxyquinolinato) aluminium and 1,3,5-tris (1-phenyl-1H-benzimidazole-2-yl) benzene exhibit the SOP phenomenon, where permanent dipoles naturally orient perpendicular to the substrate in average, generating surface potentials of several volts over 100nm film thickness. By utilizing these polar organic molecules as electrets, we have developed E-VEHs that require no charging process. This paper introduces the operational mechanism of SOP-based E-VEHs and discusses design guidelines for performance enhancement using numerical simulations.