# Strategic Development of Piezoelectric Nanogenerator and Biomedical Applications
## 3 Strategies
### Hybrid Structures
An average peak power density of 1.864 mW/cm\({}^{2}\) was achieved. In 2020, [PERSON] et al. [122] utilized Ca-doped BTO to fabricate a piezo-tribo-HNG (Figure 10A(a)), thereby demonstrating a simple fabrication technique. Ca-BTO micro-particles (MPs) were synthesized via a solid-state reaction. Subsequently, the synthesized Ca-BTO MPs were mixed with the PDMS, and the PDMS/Ca-BTO composite film was incorporated as the active material in the assembly (Figure 10A(b)). Next, the developed composite film was laminated on Al tape and glued with a flexible acrylic substrate. Al was employed as a positive triboelectric material, and the top electrode was prepared by attaching a piece of Al to an acrylic substrate. Finally, the top and bottom components were fastened using cellophane tape to form an arc-shaped Ca-BTO-based HNG. The fabricated device exhibited a closed-circuit current and open-circuit voltage of 34 uA and 550 V, respectively (Figure 10A(c)), with a maximum power density of 23.6 W/m\({}^{2}\). Recently, investigations on the synergetic effects of morphology, doping, and hybrid structures have been trending in HNG. For example, [PERSON] et al. [123] fabricated an HNG device based on Y-doped ZnO nanoflowers. Y-ZnO nanoflowers were synthesized and composited with PDMS using a wet chemical precipitation method. An HNG device was fabricated by attaching the top and bottom components. Both strategies were exploited further to enhance the performance of the HNG. An output voltage and current of 247 V and 7 uA, respectively, were achieved. In addition, several studies on piezo-pyro-HNGs have been reported. Most piezoelectric materials exhibit pyroelectric properties. [PERSON] et al. [124] demonstrated the fabrication of a piezo-tribo hybrid by embedding an MXene-based bifunctional conductive filler, which boosted the performance. As the incorporation of an active material eventually reduces the flexibility of polymer, in that study, the authors added a conductive filler which helped to maintain a low concentration of ceramic filler and a high dielectric constant. They utilized MXene as a conductive filler, BaTiO3 as an active piezoelectric material, and PDMS as a polymer matrix. the F atoms present in the MXene improved the electrical output generation, which was theoretically and experimentally analyzed. The fabricated device provided an output voltage of 80 V, with an output current of 14 uA. The fabricated device was utilized for a human manipulation system and a material detection system. [PERSON] et al. [125] fabricated a device based on the coupled piezoelectric-triboelectric-pyroelectric effect Figure 10B(a). The fabricated device was able to simultaneously harvest mechanical, thermal, and solar energy. The fabricated device exhibited a significant improvement in output performance. The fabricated device consisted of three parts: PZT with piezoelectric, pyroelectric, and photoelectric active material. The polyamide (nylon) acted as a flexible vibrating film to generate a triboelectric effect; additionally, it exerted strain on the neighboring PZT film. Ag was used to form the bottom electrode, whereas ITO film, combined with Ag nanowire/PDMS attached to the PZT film, acted as the top electrode. A radiator, an adjacent temperature device, acted as the final thermoelectric component. This multi-effect device harvested energy from multiple sources and exhibited the potential to deliver superior performance (Figure 10B(c)).