 Eem contains QSC,max that is proportional to the triboelectriﬁcation area A.Therefore, to exclude the effect of the TENG size on the output energy, the area A should be placed in denominator of this term and then the term formula_26 determines the merits of TENG.QSC,max, VOC,max and V max’ are all proportional to the surface charge density σ.