Carrier Separation Boosts Thermoelectric Performance of Flexible n‐Type Ag₂Se‐Based Films

Abstract Owing to promising room‐temperature thermoelectric properties, n‐type Ag₂Se has been considered as an alternative for Bi₂Te₃. Herein, a carrier separation strategy is realized by compositing an insulating electron donor, polyethyleneimine (PEI), with the n‐type Ag₂Se. Inhomogeneous distribution of PEI can attract the minority carriers (holes) in the n‐type Ag₂Se matrix, while the separated minority carriers can avoid significant scattering of the main carriers based on coulomb repulsion, leading to record‐high carrier mobility of 1551.99 cm² V⁻¹ s⁻¹ and an improved S²σ of 22.39 µW m⁻¹ K⁻² at 300 K for 6 mol% PEI/Ag₂Se composite film. Moreover, with PEI acting as a binder, the resistance of 6 mol% PEI/Ag₂Se composite film only increases by 6.5% after bending 1000 cycles at the radius of 6 mm, showing high stability. The assembled flexible device based on 6 mol% PEI/Ag₂Se composite films exhibits an excellent power density of 73.93 W m⁻² at a temperature difference of 50 K, showing potential applications in powering generation for wearable electronics.