Fundamental research on the effective contact area of micro-/nano-textured surface in triboelectric nanogenerator

The triboelectric nanogenerator (TENG) is a new energy technology to convert mechanical energy into electricity based on contact electrification and electrostatic induction. An effective way to improve power generation of TENG is to increase the effective contact area through introducing micro-/nano-textures onto the contact surface. However, the definition and quantitative analysis on the effective contact area of micro-/nano-textures is still in doubt so that the design of surface texture to improve the output of TENG is lack of theoretical basis. In this paper, an adhesive contact model considering textures is 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 applied force and texture size on the effective contact area and open-circuit voltage. On the other hand, the pyramid textured surfaces of TENG are fabricated through lithography, wet etching and replication techniques, the test platforms of contact area and electrical output for TENGs are constructed as well, and results from simulation and experiment are compared at last. It is shown that, firstly, the four sides of pyramid texture are involved in the contact electrification and therefore the effective contact area should be the sum of the pyramid lateral area involved in contact when contact only happens in texture region, or the sum of pyramid lateral area and flat area involved in contact when contact happens in both texture and flat regions. Secondly, under lighter loading, the open-circuit voltage of TENGs with pyramid textures increases due to the increase of contact area, while under heavier loading, the open-circuit voltage remains stable due to the unchanged contact area. In addition, the contact area and open-circuit voltage of TENGs will increase with increased texture pitch under lighter applied force while decrease with increased texture pitch under heavier applied force. This study reveals the correlation between the contact area and electrical performance of TENG with textured surfaces and provides theoretical basis for texture design of TENG.