Synthesis of fluorinated polyimide towards a transparent triboelectric nanogenerator applied on screen surface

It is of great commercial prospect to apply triboelectric nanogenerators (TENGs) to harvest mechanical energy from contact and sliding motion between fingers and the touch screen surface. For this application, the triboelectric material is required to have not only strong electronegativity but also transparency, low adhesion and low friction. Among the existing transparent triboelectric materials, polydimethylsiloxane (PDMS) is so soft and adhesive that it is not suitable to be applied on touch screens, and polyethylene terephthalate (PET) has weak electronegativity. Therefore, a transparent fluorinated polyimide (PI) film with a light transmittance of 90% is synthesized, and its electrical performance, adhesive and tribological properties are studied in this study. The electrification performance of the fluorinated PI increased by 60-70% compared to that of Kapton. In addition, fluorination reduces the adhesion and friction coefficient of the film, thus reducing the touch resistance and improving its durability in triboelectrification. Finally, the transparent PI-based TENG attached on the cellphone screen can effectively harvest mechanical energy to charge the capacitor with a voltage increment of 0.18 V with every tap on the screen surface.