Microstructurally Tailored Thin β‐Ag 2 Se Films toward Commercial Flexible Thermoelectrics

Aiming to overcome both the structural and commercial limitations of flexible thermoelectric power generators, an efficient room‐temperature aqueous selenization reaction that can be completed in air within less than 1 min, to directly fabricate thin β‐Ag 2 Se films consisting of perfectly crystalline and large columnar grains with both in‐plane randomness and out‐of‐plane [201] preferred orientation, is designed. A high power factor (PF) of 2590 ± 414 µW m −1 K −2 and a figure‐of‐merit ( zT ) of 1.2 ± 0.42 are obtained from a sample with a thickness of ≈1 µm. The maximum output power density of the best 4‐leg thermoelectric generator sample reach 27.6 ± 1.95 and 124 ± 8.78 W m −2 at room temperature with 30 and 60 K temperature differences, respectively, which may be useful in future flexible thermoelectric devices.