Thermoelectric Properties of Bare and Nonconductive Polymer-Encapsulated Sb₂Te₃-MWCNT Hybrid Networks and Their Application in Flexible Heat-to-Power Conversion Devices

In this work, thermoelectrical properties of flexible thermoelectric films fabricated by the encapsulation of multiwalled carbon nanotube-antimony telluride (Sb₂Te₃-MWCNT) hybrid networks with different Sb₂Te₃:MWCNT mass ratios in polydimethylsiloxane (PDMS) were studied for the first time. Sb₂Te₃-MWCNTs were synthesized by the direct physical vapor deposition of Sb₂Te₃ nanostructures on the MWCNT network, spray-coated on a flexible polyimide substrate, and encapsulated in PDMS using a drop-casting technique. A study of electrical and thermoelectric properties of Sb₂Te₃-MWCNT hybrid networks before and after encapsulation revealed that encapsulation effectively preserves the properties of the hybrid networks and improves their durability under repetitive bending, showing deviations in resistance not exceeding 0.5% of the initial value during 100 repetitive bending cycles down to a 3 mm radius. Encapsulated Sb₂Te₃-MWCNT networks showed the thermoelectric power factor (PF) reaching 9.5 μW·m^-1 K^-2, which is ∼3 orders of magnitude higher than the values of PF showed previously by the composites prepared by mechanical mixing of the Sb₂Te₃-MWCNT hybrid networks with a nonconductive polymer. PDMS-encapsulated Sb₂Te₃-MWCNT hybrid networks in combination with previously reported PVA-encapsulated Bi₂Se₃-MWCNT hybrid networks were used to assemble 4-leg-pair flexible thermoelectric generators, where leg pairs were connected in series or parallel. Both types of generators showed stable performance with different external resistances connected in the circuit and reached an output power of ∼7-10 μW·cm^-2 and an output current of ∼1-5 μA. These parameters illustrate the significant potential of the presented PDMS-encapsulated Sb₂Te₃-MWCNT hybrid networks as building blocks for custom flexible devices for micro- and nanopower applications.