Toward inorganic flexible π-shaped thermoelectric generators with high output power density: From materials to devices

Flexible thermoelectric generators (f-TEGs) have emerged as among the most promising candidates to address the persistent energy supply challenges associated with wearable electronics. To achieve practical applications of inorganic π-shaped f-TEGs rapidly requires enhancing their output power density, which represents the primary and pivotal objective. This review distills three main factors that govern output power density, namely, the power factor of thermoelectric materials, the geometric and packaging configurations of f-TEGs, as well as the effective temperature gradient across the f-TEGs. Further, the principal optimization strategies adopted for these factors over recent years are outlined. The strategies encompass approaches such as carrier concentration modulation, carrier scattering mechanism regulation, and energy band engineering to enhance the power factor, finite element simulations and numerical computations for optimizing geometric structure and packaging, and the integration of hydrogels and phase change materials into flexible heat sinks to establish and maintain sufficiently large temperature differences. Additionally, the discussion extends to the flexibility of inorganic materials and generators themselves. Finally, the concluding section addresses the challenges and critical issues confronting the development of flexible thermoelectric materials and generators.