Key Takeaways & Executive Findings
- •• • f-TE devices enable multimodal sensing of temperature, pressure, and strain simultaneously, with demonstrated applications in deep-learning-assisted sign language and object recognition (Yang et al., Chem Eng J, 2024, 488: 150816), indicating high sensitivity and specificity for human-machine interfaces. • • Self-powered f-TE systems have been integrated with wireless wearable platforms for real-time physiological and biochemical monitoring (An et al., Adv Funct Mater, 2023, 33: 2303361), achieving continuous health tracking without external power sources, a critical step toward autonomous wearables. • • Thermoelectric gel-based sensors have achieved self-powered facial perception for expression recognition and health monitoring (Cui et al., ACS Sens, 2024, 10: 537–544), demonstrating the potential for non-invasive diagnostic tools with high temporal resolution. • • Stretchable and integratable thermoelectric nanofiber yarns have been continuously manufactured for human body energy harvesting and self-powered motion detection (He et al., Chem Eng J, 2022, 450: 137937), offering scalable production routes for wearable energy solutions.
Abstract
Flexible thermoelectrics (f-TEs) are being developed rapidly due to their unique advantages, such as direct conversion between electricity and thermal energy, compatibility with curved heat sources, and ease of integration. Over the past decade, significant progress has been made in enhancing the overall performance of f-TE materials and devices, particularly in terms of output power, mechanical flexibility, and durability. Recent research efforts are increasingly focused on translating these advancements into practical applications across diverse fields. For example, f-TE-based multimodal sensors are capable of simultaneously detecting temperature, pressure and strain. In biomedicine, f-TE generators are being explored for wound healing, antibacterial therapy, and neural modulation. Furthermore, f-TE devices show promise in personalized thermal management and hybrid energy harvesting systems. This review moves beyond material preparation and device optimization to focus on the expanding multifunctional applications of f-TEs. We provide a broad perspective by comprehensively exploring the latest progress of f-TEs in intelligent sensing, biomedicine, personalized thermal management, and multifunctional hybrid systems. Key challenges are also discussed, including the development of high-performance flexible devices, robust bio-interfaces, ensuring long-term stability, and achieving intelligent integration with data-driven algorithms and multimodal platforms. Finally, we offer insights into future directions for f-TEs, pointing toward next-generation intelligent and bio-integrated flexible electronics.
1. Introduction
Flexible thermoelectrics (f-TEs) have emerged as a transformative technology for harvesting low-grade heat from the human body and ambient sources, yet their commercial adoption has been hindered by the trade-off between thermoelectric efficiency (ZT) and mechanical compliance. Traditional rigid thermoelectric modules, while achieving high ZT values, cannot conform to curved surfaces or withstand repeated deformation, limiting their integration into wearables and biomedical devices. Moreover, manufacturing processes for flexible devices often sacrifice performance for flexibility, resulting in power outputs insufficient for practical applications. The field has thus faced a bottleneck: how to achieve both high energy conversion efficiency and robust mechanical flexibility without compromising scalability.
This review addresses this bottleneck by systematically analyzing recent breakthroughs in f-TE materials, device architectures, and multifunctional applications. Notably, the integration of f-TEs with advanced manufacturing techniques such as printing and laser processing has enabled the creation of stretchable and wrinkle-resistant designs that maintain performance under strain. Furthermore, the convergence of f-TEs with machine learning and multimodal sensing has unlocked new capabilities in intelligent health monitoring and human-machine interfaces. By focusing on application-driven design, this review provides a roadmap for translating laboratory-scale innovations into commercially viable, next-generation wearable and integrated systems.
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Sihui Li, Wantian Zhang, Li-Dong Zhao, Yao Lu (2026). Multifunctional Flexible Thermoelectric Devices for Next-Generation Wearable and Integrated Systems. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3888-9
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Frequently Asked Questions
What are the primary failure mechanisms of flexible thermoelectric devices under repeated mechanical stress, and how can they be mitigated?
Under cyclic bending or stretching, f-TE devices often suffer from delamination at material interfaces, cracking of brittle inorganic thermoelectric legs, and fatigue of conductive interconnects. Mitigation strategies include using intrinsically stretchable materials like conductive polymers and elastomeric composites, designing serpentine or wrinkled geometries to accommodate strain, and employing robust encapsulation layers. For instance, avian bone-inspired super fatigue resistant MXene-based aerogels have demonstrated enhanced durability (Ren et al., Adv Funct Mater, 2024, 34: 2403091), indicating that bio-inspired structural designs can significantly improve mechanical robustness.
How do f-TE devices achieve self-powered operation for health monitoring, and what are the typical power outputs?
f-TE devices convert body heat into electrical power via the Seebeck effect. Typical power outputs for wearable f-TE generators range from microwatts to milliwatts per square centimeter, depending on the temperature gradient and device efficiency. For example, body heat powered wirelessly wearable systems have been demonstrated for real-time physiological monitoring (An et al., Adv Funct Mater, 2023, 33: 2303361), achieving sufficient power for low-power sensors and wireless data transmission. The integration of energy harvesting and storage components, such as supercapacitors or batteries, enables continuous operation.
What are the scalability challenges in manufacturing f-TE devices, and what progress has been made?
Scalability is challenged by the high cost of high-performance thermoelectric materials (e.g., bismuth telluride) and the complexity of patterning and assembling flexible substrates. However, recent advances in printing techniques, such as screen printing and inkjet printing, allow for roll-to-roll production of f-TE modules. Continuous manufacture of stretchable thermoelectric nanofiber yarns has been reported (He et al., Chem Eng J, 2022, 450: 137937), demonstrating a scalable route for textile-based f-TEs. Cost reduction remains a key issue, but the use of organic and composite materials may offer a more economical alternative.
How do f-TE-based sensors achieve multimodal detection (temperature, pressure, strain) without cross-talk?
Multimodal f-TE sensors often employ separate sensing elements or decouple signals via machine learning algorithms. For instance, thermoelectric gels can detect temperature via the Seebeck voltage, while pressure and strain are measured through changes in resistance or capacitance. By integrating multiple sensing mechanisms and using data fusion techniques, cross-talk can be minimized. Deep learning models have been used to accurately classify and quantify different stimuli, as demonstrated in sign language and object recognition systems (Yang et al., Chem Eng J, 2024, 488: 150816).
What are the key challenges for clinical translation of f-TE devices in wound healing and neural modulation?
Clinical translation requires robust bio-interfaces that are biocompatible, non-toxic, and stable in physiological environments. f-TE devices must also maintain performance over extended periods and be sterilizable. For wound healing, the electric field generated by f-TEs must be carefully controlled to promote cell migration and proliferation without adverse effects. Studies on endogenous electric fields in wound healing (Nuccitelli, Curr Top Dev Biol, 2003, 58: 1–26) provide a basis for designing f-TE stimulation parameters. Long-term stability and regulatory approval are major hurdles, but recent advances in flexible, adhesive, and anti-freezing hydrogels (Zhao et al., Chem Mater, 2024, 36: 8141–8158) show promise for safe and effective bio-integration.
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