Organic thermoelectric thin films with large p-type and n-type power factor

P- and n-type thermoelectric (TE) materials were prepared by using a layer-by-layer method. Assembled nanocomposites displayed high TE properties. For the p-type nanocomposites, polyaniline (PANi)/graphene-poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/PANi/carbon nanotubes (CNT)-PEDOT:PSS quadlayers (QL) were assembled by immersing a substrate alternately to aqueous solutions of these charged materials. Various concentrations of three types of CNT (single-walled, double-walled (DWNT), and multi-walled) and two different surface areas of graphene (300 and 750 m² g⁻¹) were investigated. The best QL films, assembled with graphene and DWNT, exhibit a power factor (PF = S² σ) of 3050 µW m⁻¹ K⁻² at room temperature, which is among the highest values for a fully organic material. In an effort to improve TE properties in n-type organic thin films, hydrazine is introduced to the films in which DWNT, stabilized by polyethylenimine (PEI), is alternately deposited with graphene, stabilized by polyvinylpyrrolidone (PVP). After doping these films for 5 min with hydrazine, electrical conductivity and Seebeck coefficient significantly increase. An 80 DWNT-PEI/graphene-PVP bilayer film achieves a PF as high as 380 µW m⁻¹ K⁻² at room temperature, exhibiting a twofold improvement relative to that of un-doped films. In light of the growing interest in organic thermoelectric nanocomposites, this study provides an effective means to achieve high performance that will allow these unique materials to replace inorganic semiconductors in some applications.