Flexible wearable devices based on self-powered energy supply

Wearable devices have emerged as a transformative technology in health monitoring, human-machine interaction, and the Internet of Things (IoT). However, their dependence on rigid, bulky, and conventional batterybased power systems imposes significant limitations. Self-powered systems that leverage energy harvesting technologies, such as piezoelectric nanogenerators (PENG), triboelectric nanogenerators (TENG), and thermoelectric nanogenerators (TEG), to offer a sustainable alternative by converting energy from human motion, temperature gradients, and environmental sources into electrical power. This review discusses the energy conversion mechanisms, working principles or modes and necessary materials of piezoelectric, triboelectric, and thermoelectric nanogenerators, highlighting their fundamental properties, structural optimization and groundbreaking achievements that enhance the performance of these materials. Furthermore, integration strategies for combining nanogenerators with supercapacitors are classified and underlined to construct special self-powered systems that seamlessly integrate energy harvesting, energy storage, and circuit management. Importantly, we expound the excellences and highlight their specific features or functions of these cutting-edge technologies necessitated in various applications, e.g., real-time health monitoring, motion tracking, and disease treatment are also outlined. Beyond that, an in-depth discussion on the existing challenges that current self-powered wearable device research encounters, including energy conversion efficiency, stability, and material durability is proceeded. Accordingly, revolutionary solutions and different perspectives from material innovation, technology integration, and interdisciplinary collaboration that cater to certain application demands are proposed to address these obstacles or challenges, which are anticipated to propel the future development and deployment of efficient, environmentally sustainable, next-generation self-powered wearable devices.