This review offers a critical overview of recent developments in lead-free piezoelectric materials and flexible device architectures for self-powered wearable and Internet of Things systems. It examines the scientific and technological rationale for replacing conventional battery-dependent power sources with ambient mechanical energy harvesters, and it evaluates the relative merits of inorganic ceramics, organic polymers, and composite systems in achieving efficient electromechanical conversion under practical operating conditions. The discussion further considers compositional tuning, phase boundary engineering, microstructural optimization, and device-level integration as key strategies for improving piezoelectric output, mechanical compliance, durability, and manufacturability. By connecting fundamental materials design with application-driven device requirements, the review identifies the principal challenges and emerging directions necessary for the realization of reliable, scalable, and sustainable electronic platforms.

The rapid evolution of wearable technology has driven a surge in demand for sustainable, self-powered electronic devices. Flexible thermoelectric materials, capable of converting body heat into electricity, have emerged as a promising solution for powering next-generation wearables. This review comprehensively examines recent progress in organic (polymer-based) and hybrid thermoelectric materials, focusing on their design, fabrication, and integration into flexible architectures suitable for conformal contact with human skin. Key developments include advanced doping strategies, post-treatment techniques, and composite engineering, particularly in conductive polymers such as PEDOT: PSS and P3HT, which have significantly enhanced power factors and mechanical flexibility. Additionally, the integration of high-performance inorganic materials into stretchable systems has further elevated device efficiency and durability. The review highlights breakthroughs, ongoing challenges, and future opportunities in realizing practical, scalable, and high-efficiency wearable thermoelectric generators for sustainable energy harvesting applications.

Citations

• Design and optimization of all-segmented thermoelectric legs based on Bi2Te3 and SnTe for wide-range energy harvesting
  Hyejeong Choi, Momanyi Amos Okirigiti, Nagamalleswara Rao Alluri, Jong Min Park, Donghyun Shin, Ho Seong Lee, Kyung Tae Kim, Changyeon Baek, Min-Ku Lee, Gyoung-Ja Lee, Kwi-Il Park
  Journal of Power Sources.2026; 691: 240981.     CrossRef