Two voltages in contact-separation triboelectric nanogenerator: From asymmetry to symmetry for maximum output

The output voltage is an important parameter to evaluate performance of triboelectric nanogenerator (TENG). However, the voltage for contact-separation TENG is hardly to reach a higher value and commonly gives an asymmetric alternating voltage (current). When the upper electrode operates from separation to contact state, the voltage is mainly related to dielectric film thickness (Low voltage), while it operates from contact to separation state, the voltage is mostly depended on separate distance (High voltage). It is found that the output voltage is limited by the asymmetrical voltages because the Low voltage hardly pushes charges fully from one electrode to another electrode in large load situation. Two strategies are found. By increasing dielectric film thickness symmetrical output voltages are obtained and 2.7 times output energy are achieved. By using half-wave circuit to eliminate the low voltage restriction, 16.5 kV high voltage and 5 times output energy (1.862 mJ per cycle) are achieved. The improved voltage mechanism of contact-separation TENG in this work provides a basic scientific method for maximum energy output, which also can be used in other device improvement.