where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity. Having both n-and p-type TE materials is an essential requirement for building an efficient TE device. [3] So far the use of organic-inorganic nanocomposites, where electrically conductive p-or n-type polymer is used as a matrix for supporting a network of carbon nanotubes (CNTs) and/or inorganic TE nanostructures as flakes, nanoplates, or nanowires has shown the greatest potential for engineering efficient flexible TE devices. [4] CNTs have been reported to be one of the most promising components for producing p-type flexible TE nanocomposites. [5][6][7][8][9] However, application of CNTs in n-type TE composites is complicated due to necessity of CNTs pretreatment (annealing under high vacuum) for oxygen desorption and transition of their conductivity type from p-type (arising from extrinsically induced by the adsorbed oxygen hole-like concentration [10] ) to n-type, and further isolation from ambient environment (air) to prevent oxygen adsorption. This significantly complicates the practical use of n-type CNTs in ambient conditions (air). Another drawback of n-type conductive polymers and their based composites is poor stability in air, resulting in decrease of electrical conductivity by orders of magnitude when exposed to air even for a short period of time. [10] The use of organic-inorganic nanocomposites has shown the greatest potential for engineering efficient flexible thermoelectric devices. In this work, a novel approach of encapsulation of as-grown bismuth selenide-multiwalled carbon nanotubes (Bi 2 Se 3 -MWCNT) hybrid network in polyvinyl alcohol for fabrication of n-type flexible thermoelectric films is demonstrated as a successful alternative to the mechanically mixed counterparts. The developed stable flexible n-type thermoelectric material has a Seebeck coefficient and power factor at room temperature as high as −85 μV K −1 and 0.4 μW m −1 K −2 , and figure-of-merit, exceeding the value shown by the mixed counterpart by ≈2 orders of magnitude, while requiring 3-4 times less inorganic material in comparison with mixed composites. Charge carrier transport mechanisms and contribution of Bi 2 Se 3 and MWCNT components of not encapsulated and encapsulated hybrid networks to the total Seebeck coefficient, electrical conductance, and power factor are studied. In addition, the fabricated flexible thermoelectric films show good environmental stability at relative humidity levels up to 60%, as well as great mechanical and electrical stability with the increase of resistance within 0.5% and deviations of the Seebeck coefficient within 2% from the initial value during the 100 repetitive bending cycles.

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