Sandwich Engineering Advances Ductile Thermoelectrics

Flexible thermoelectrics offer the possibility of utilizing human body heat to generate electricity, enabling self-powered wearable electronics. Ductile and plastic semiconductors are promising materials for flexible thermoelectrics due to their inherent ductility and tunable electrical properties. However, balancing ductility with high thermoelectric performance remains challenging, especially for n-type materials. Here, a novel n-type ductile Ag₂(S, Se)-Ag₂Se sandwich-like thermoelectric film is designed with different functional layers, where the Ag₂(S, Se) core layer provides ductile deformation ability and low thermal conductivity, while epitaxially grown highly oriented Ag₂Se shell layers ensure superior electrical transport performance. This architecture achieves a record high figure-of-merit near room-temperature range, 0.91 at 323 K, among n-type ductile semiconductors while preserving excellent flexibility. Additionally, a flexible in-plane device fabricated from this material delivers an exceptional power density of 26.5 W m⁻² at a temperature difference of 50 K, demonstrating its great application potential for wearable electronics. Importantly, such novel sandwich engineering can pave the way to alleviate the compromise between thermoelectric performance and ductility in inorganic semiconductors.