Recent progress in cellulose-based flexible thermoelectric devices: Materials, designs, mechanisms, and applications

The rapid advancement of wearable electronics has underscored the importance of flexible thermoelectric (TE) devices as efficient platforms for continuous energy harvesting from body heat or environmental temperature gradients, due to their excellent adaptability to complex and dynamic surfaces. Among various candidates, cellulose-based materials derived from renewable biomass stand out for their outstanding processability, sustainability, and environmental compatibility, making them ideal scaffolds for flexible TE systems. Recent developments reveal that combining cellulose matrices with conductive polymers, carbon nanomaterials, and inorganic TE components can yield hybrid composites that simultaneously exhibit high thermoelectric performance and mechanical flexibility. Such innovations highlight the significant potential of cellulose materials for sustainable energy conversion and self-powered wearable applications. This review critically summarizes the latest progress in the design, fabrication, and integration of cellulose-based thermoelectric materials and devices, with a particular focus on processing strategies and performance enhancement mechanisms. Furthermore, it systematically discusses the existing challenges in material selection, thermal-electrical transport optimization, environmental degradability, and scalable manufacturing. Through this comprehensive analysis, the review aims to provide deep insights and practical guidance for developing next-generation, high-performance, and eco-friendly thermoelectric materials to advance sustainable energy harvesting technologies.