Synergistic Bi–Te Antisite Defects and Crystalline‐Amorphous Hybrid Structure Enable Record‐High Thermoelectric Performance in Flexible Bi ₂ Te _2.7 Se _0.3 Films

ABSTRACT Flexible n‐type Bi 2 Te 3 thin films are highly promising for wearable thermoelectric devices but still face major challenges in achieving a high room‐temperature figure of merit ( ZT ) while maintaining performance under mechanical deformation. Here, we demonstrate that the synergistic tuning of Bi–Te antisite defects and crystalline‐amorphous hybridization effectively overcomes these limitations. Bi 2 Te 2.7 Se 0.3 thin films were fabricated via thermal evaporation followed by post‐annealing, during which antisite defect formation modulates carrier concentration, while crystalline‐amorphous hybridization enhances Hall mobility and phonon scattering. As a result, the optimized films achieve a high power factor of 35 µW cm −1 K −2 and a remarkable ZT of 1.48 near room temperature, surpassing most reported n‐type flexible thermoelectric thin films. A flexible thermoelectric device assembled from 162 pairs of these thin films delivers a power density of 114 µW cm −2 and a normalized power density of 4.58 µW cm −2 K −2 under a small temperature difference of 5 K. When attached to the human body, the device generates an output voltage of 333 mV, sufficient to drive common wearable electronics. This defect‐phase co‐regulation strategy provides a general and scalable design pathway for achieving high‐performance flexible thermoelectric materials and devices.