The space tribo-charge region and equivalent charge plane model in triboelectric nanogenerators

Abstract

Recently, triboelectric nanogenerators (TENGs) have emerged as a rapidly growing technology for energy harvesting and self-powered sensing. Enhancing the output performance of TENGs requires a thorough understanding of their physical mechanisms. To clarify the inherent mechanisms of TENGs, formal electrostatic frameworks have been introduced to predict the output voltage of TENGs. However, these approaches still have certain limitations, because the triboelectric charge has been treated as a zero-thickness surface charge, which has been demonstrated to be overly idealistic by experimental data. Here, we propose a space tribo-charge region (STCR) model, which captures the finite thickness distribution of the triboelectric charge, replacing the traditional zero-thickness surface charge model, to more accurately describe the electrostatic behavior of contact–separation mode TENGs (CS-TENGs). As CS-TENGs typically operate under low frequencies, the electric field generation by the STCR is treated as an electrostatic phenomenon. An equivalent charge plane (ECP) model was also proposed to analytically derive the electric field distribution generated by the STCR. The formation process of the STCR model and its induced electrostatic field/potential distribution are investigated using a series of CS-TENGs. The dielectric layers of the examined CS-TENGs consist of fixed-thickness polydimethylsiloxane (PDMS) on one side and variable-thickness fluorinated ethylene propylene (FEP) layers ranging from 15 μm to 100 μm on the other side. The polarity-swapping phenomenon predicted by the STCR model was also examined. Overall, this work introduces a new perspective on how triboelectric surface charges should be treated and demonstrates how the STCR model can explain the open-circuit voltage output characteristics of CS-TENGs.