Abstract

Abstract Owing to promising room‐temperature thermoelectric properties, n ‐type Ag 2 Se has been considered as an alternative for Bi 2 Te 3 . Herein, a carrier separation strategy is realized by compositing an insulating electron donor, polyethyleneimine (PEI), with the n ‐type Ag 2 Se. Inhomogeneous distribution of PEI can attract the minority carriers (holes) in the n ‐type Ag 2 Se 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 cm 2 V −1 s −1 and an improved S 2 σ of 22.39 µW m −1 K −2 at 300 K for 6 mol% PEI/Ag 2 Se composite film. Moreover, with PEI acting as a binder, the resistance of 6 mol% PEI/Ag 2 Se 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/Ag 2 Se 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.