Inherent asymmetry of the current output in a triboelectric nanogenerator DharmasenaIshara 2020 © 2020 Elsevier Ltd Triboelectric Nanogenerators (TENGs) are a leading candidate in powering the next generation of flexible and mobile electronics. However, the sporadic variations of output current and the asymmetry (variations in magnitude) between the current peaks are some of the key issues of this technology, impeding the reliable operation, consistency and the reproducibility of their outputs. Investigating the causes for this asymmetric and sporadic behaviour is therefore critical in developing optimised TENG devices. This study, for the first time, comprehensively investigates the asymmetry between the positive and negative current peaks (corresponding to ascending and descending motion half cycles) and the underlying reasons for this phenomenon. The operation of the TENG is studied in contact and non-contact operating modes, revealing a number of new findings on the current output generation and its optimisation, in order to minimize their peak variations and to enhance the power output. Finally, the significance of this study on TENGs for self-powered sensing, energy harvesting, device characterisation and standardisation is discussed, leading towards sustainable future applications.