Fig. 4. “Four-ports” methodology for evaluating the charge output.

a Schematic of the “four-ports” methodology for evaluating the charge output of the OCT-TENG. b Charge accumulation measured by the “four-ports” method. c charge on the FEP surface $Q_1$, charge on the PC surface $Q_2$, and the output charge of the OCT-TENG $Q_2-Q_1$ measured by the “four-ports” method. d Measured $Q_1$, $Q_2$ and $Q_2-Q_1$ with various material systems. (A@B/C refers to the tribo-surface of the slider as A and that of the stator as B and C). e Current output of the OCT-TENG (full circuit shown in Fig.1a) with various material systems (load resistance: 4.7 MΩ).