Flexible Porous Ag2Se Films: From Freestanding Inorganic Films to Inorganic-Network/Organic-Skeleton Thermoelectric Generators

Silver selenide (Ag2Se) flexible films are promising near-room-temperature thermoelectric candidates for low-grade heat harvesting. However, existing Ag2Se films are generally attached on substrates, which impedes further flexibility improvement of the films and constrains the scenarios of applications. Here a cost-effective and scalable strategy is presented, which combines screen printing and annealing, for synthesizing freestanding Ag2Se inorganic films with different densities of pores. High-density pores and thin thickness endow the films with high flexibility, while films with low-density pores obtain higher power factor. Furthermore, by utilizing the porous microstructure, a composite structure consisting of a Ag2Se conductive network and an organic polydimethylsiloxane (PDMS) skeleton is fabricated, which further improves films' stability under bending and torsion. Finally, a flexible thermoelectric generator comprising five Ag2Se/PDMS legs and encapsulated PDMS outputs a voltage of 20.2 mV and a maximum power of 810 nW (the corresponding power density is 5.4 W m(-2)) at a temperature difference of 30 K, verifying potential application at near room temperature. This work offers a useful paradigm for fabricating substrate-free Ag2Se porous films with high flexibility for near-room-temperature thermoelectric applications.