Triboelectric nanogenerators (TENGs) have been highlighted as a power source for small electronic devices thanks to their relatively simple fabrication and integration with existing device structures. To increase their output power to a level sufficient for small electronic device, considerable efforts have focused on improving their output power. So far, different surface patterning methods, dielectric constant tuning, and device structures have been employed. However, these approaches are relatively complicate and the performance of TENGs is still limited by intrinsic properties of materials used.
In this work, we introduce a simple and effective way to tune the triboelectric charging sequence by adopting atomic level chemical surface functionalization. To this end, the synthetic halogenated (Cl, F, and Br)-molecules were functionalized onto polyethylene terephthalates (PETs) to render negative charging surface. For the triboelectrically positive side, on the other hand, the surfaces of PETs were functionalized using several aminated-molecules. Using Kelvin probe microscopy, electrometer, and density functional calculation, thorough investigation has been made to understand the charging behavior of functionalized surfaces. Our results show that wide spectrum of triboelectric charging can be clearly formed by the proposed methods. Noticeably, the TENGs with functionalized using the pair (Cl-PET:PEI(b)-PET) exceed the output voltage of ~520 V and current density of ~110 mA/m2, corresponding power density of ~55 W/m2, which is one of the highest values reported to date. Besides, by providing wide choices of surface functionalization, friction surface can be rendered to have different triboelectric properties, allowing to adopt this technique to develop triboelectric sensors. This works introduced the simple chemical surface method, which can be adopted for developing energy harvesting devices and sensors based on the triboelectric effect.