Comprehensive contact analysis for vertical-contact-mode triboelectric nanogenerators with micro-/nano-textured surfaces

The triboelectric nanogenerator (TENG) is a new energy technology to convert mechanical energy into electricity based on contact charging and electrostatic induction. To increase the effective power generation in a limited device size, micro-/nano-textures are often designed at the contact surfaces. As the contact region decreases to micro/nano scale, adhesive forces such as van der Waals and electrostatic forces become dominant. However, there is currently no comprehensive model including micro-/nano-textures and the above adhesive forces, and thus the selection and design of textures are still lack of theoretical guidance. In this paper, the numerical contact and electrical models considering van der Waals and electrostatic forces are established, and the computational methods such as inexact Newton method, bi-conjugate stabilized (Bi-CGSTAB) method and fast Fourier transform (FFT) technique are employed to quantitatively analyze the effects of charge densities, applied loads, texture shapes and sizes on both contact and electrical performance. It is shown that the electrostatic force can be ignored when the charge density is small, while with large charge density, the electrical performance is significantly overestimated if the electrostatic forces are neglected. Among the four selected types of textures (pyramid, cone, cylinder and cube), the pyramid and cube textures are found to provide the larger output voltage under different applied loads, and also the optimal sizes for high voltage are presented, respectively. This study can provide the guideline for the texture design of high power generation TENGs.