Enhancing energy harvesting performance of bilayered parylene triboelectric nanogenerators through interfacial polarization

Self-powered multifunctional devices have found applications in various fields including internet of things, smart robotics, and wearable haptic technologies. Triboelectric Nanogenerators (TENGs) are particularly noteworthy as they operate based on simple triboelectrification between contacting materials, and provide significantly higher output performance compared to other energy harvesting devices. In this study, we introduce soft bilayer structured films to significantly enhance the interfacial polarization and the resulting triboelectric output performance. The soft bilayer film is composed of two layers: a layer of parylene derivatives with different functional groups and a composite layer of polydimethylsiloxane (PDMS) embedded with multi-wall carbon nanotube (MWCNT). The parylene-deposited MWCNT-PDMS films effectively induce interfacial polarization due to the difference in permittivity between the parylene derivatives and MWCNT-PDMS, resulting in substantial improvement in triboelectric performances. Moreover, the specific functional groups present in the parylene monomers significantly affect the triboelectric polarity of the parylene-deposited bilayer films. The bilayer films deposited with parylene including fluorine, methyl hydroxyl, and hydroxyl groups, which improve the electron withdrawing capability, exhibit negative triboelectric properties. In contrast, the bilayer film deposited with parylene including methyl amine group, which enhances the electron-donating ability, exhibits a positive triboelectric property. Owing to the highly improved interfacial polarization in the parylene-deposited bilayer films, our TENG consisting of paired bilayer films demonstrates superior output performance (4.57 W/cm2 and 10.28 W/cm2 for contact and separation step, respectively) compared to devices based solely on single layers of parylene-or PDMS (less than a few of mW/cm2). Our approach to designing layer-structured dielectric films offers a simple yet effective method to significantly enhance the output performance of self-powered flexible devices through improved polarization.