High Thermoelectric Performance of Flexible and Free-Standing Composite Films Enabled by 3D Inorganic Ag(2)Se Conductive Networks Filled with Organic PVDF.

Herein, a flexible and free-standing (substrate-free) PVDF/Ag(2)Se (Polyvinylidene fluoride) composite film was successfully fabricated through a combination of drop-casting and heat treatment. It was observed that when the drop-casted PVDF/Ag(2)Se composite film was heated above the melting point of PVDF, the small and separated Ag(2)Se crystalline grains in the composite film grow and interconnect to form a three-dimensional (3D) conductive network to increase the carrier mobility, while the molten PVDF effectively fills the network voids to enhance the flexibility and mechanical strength. As a result, both the electrical conductivity and Seebeck coefficient of the composite films were significantly enhanced after heat treatment. The power factor of the PVDF/Ag(2)Se composite with a mass ratio of 1:4 at room temperature reached 488.8 μW m(-1) K(-2), among the best level of Ag(2)Se- or PVDF-based flexible and free-standing composite films. Bending tests demonstrated the superior flexibility of the hybrid film, with the electrical conductivity decreasing by only 10% after 1000 bending cycles. Additionally, a five-leg thermoelectric device achieved an impressive output power density of 1.75 W m(-2) at a temperature difference (∆T) of 30 K. This study proposes an innovative strategy to enhance the thermoelectric performance and free-standing capability of organic-inorganic composite films, while achieving a competitive power factor and advancing the practical application of flexible thermoelectric devices.