Research progress in flexible DC power sources based on tribovoltaic effect

Triboelectrification （TE） is a physical phenomenon that exists on the surface of almost all materials， and the TE of semiconductor materials is different from the electrification of dielectric materials.At the dynamic interface between one semiconductor and another semiconductor or a metal， mechanical friction causes the continuous breaking and rebuilding of chemical bonding between atoms at the interfaces， which could release a quantized energy that is the binding energy of two atoms （or called as bindington） to excite non-equilibrium electron-hole pairs.These electrons and holes can be separated by the built-in electric field formed at the p-n junctions （or Schottky junction， semiconductor heterojunction）， so as to output direct-current （DC） electricity in the external circuits. This phenomenon is defined as the tribovoltaic effect. It is similar to the photovoltaic effect， but the difference is the exciting energy sources. In the tribovoltaic effect， electron-hole pairs are excited by the energy released by the instantaneous transition of atoms at the interface or the energy released when new bonds are formed at the interface； while the photovoltaic effect is excited by photo energy.This article reviews the research progress of DC nanogenerators based on the tribovoltaic effect， including mechanism research， material and device design， surface modification enhancement strategies， etc. We also discuss the possible applications of tribovoltaic devices as flexible DC power sources for wearable electronics， with emphases on their device design， performance optimization，and potential application scenarios.