Fig. 5. Structure and performance of the TENG for harvesting mechanical energy. (a) Schematic diagram of the experiment setup. (b and c) Photographs of the TPU and PDMS films. (d) Working principle of the TENG. (e–h) Performance characterization of the TENG. (e) Open-circuit voltage, (f) short-circuit current, (g) transferred charge number and (h) dependence of the current and instantaneous power on the external resistance load. (The triboelectric surface between TPU and PDMS is 2 cm × 2 cm.).