Graphene has not been used as an active material in energy harvesting devices and systems. Recently, a new type of power-generating device that converts mechanical energy into electricity using triboelectricity was intensively studied. The triboelectric effect depends on various factors, such as the electron affinity, work function, friction, chemical structure, pressure, surface roughness, and humidity. A number of theoretical studies on the electrostatic behavior of graphene have been reported, and it has been concluded that graphene can store an electric charge for a period of time, which adds to its suitability for triboelectric nanogenerators. We designed and fabricated flexible transparent triboelectric nanogenerators by using monolayer, bilayer, trilayer, and quadlayer graphene. The dependence of the power output performance of the graphene triboelectric nanogenerators on the number of graphene layers is also discussed in detail in terms of the work function and friction, which arises due to different electronic relations between randomly and regularly stacked graphene layers. Furthermore, this talk will introduce a direct observation of the directional dependent piezoelectric effect in CVD grown monolayer MoS₂ using lateral piezoresponse force microscopy measurements and the piezoelectric power output from piezoelectric nanogenerators fabricated with monolayer MoS₂.