In the past decade, the research field of energy harvesting has increasingly become important, since our society is facing a problem with the depletion of fossil energy resources as well as environmental prob-lems (such as global warming, carbon dioxide emissions, and damage to the ozone layer). Energy scavenging technologies can convert existing sources of energies, such as thermal energy as well as vibrational and me-chanical energy from the natural sources of wind, waves or animal movements into electrical energy. Espe-cially, piezoelectric-based energy harvesting technologies that scavenge electricity from mechanical energy have attracted a great interest recently due to their availability in indoor or concealed environments (such as in tunnels, clothes, and in human body) without restraints. Z.L. Wang and co-workers have used piezoelectric ZnO nanowire arrays to develop nanogenerator technologies, who have demonstrated the feasibility using this type of generator to power commercial light-emitting diodes (LEDs), liquid crystal displays, and wireless data transmission. These nanogenerators can also convert tiny bits of biomechanical energy (from sources such as the movement of the diaphragm, the relaxa-tion and contraction of muscle, heartbeat, and the circulation of blood) into power sources.Piezoelectric materials, for example, ZnO, polymers (PVDF), and perovskite-type oxides (e.g. BaTiO3, PZT, SBT, BST, BiFeO3) are being studied with great interest for various applications, such as thin film capaci-tors, piezoelectric microactuators, tunable microwave devices, nonvolatile ferroelectric random access mem-ories (FRAMs), and ferroelectric field effect transistors (FeFETs). Among these piezoelectric materials, perov-skite-structured ceramic materials have drawn considerable attention due to their excellent inherent ferroelec-tric and piezoelectric characteristics. In this thesis, to demonstrate the self-powered flexible energy system, high-performance and f...