Growth mechanisms and related thermoelectric properties of innovative hybrid networks fabricated by direct deposition of Bi2Se3 and Sb2Te3 on multiwalled carbon nanotubes

Abstract

Flexible thermoelectric generators are an emerging trend in the field of waste heat conversion, as well as wearable and autonomous devices. However, the energy conversion efficiency of the state-of-the-art flexible thermoelectric devices is too low for their wide application and commercialization. In this work, n- and p-type multiwalled carbon nanotube (MWCNT)-thermoelectric material hybrid networks that may become a promising building block for the fabrication of flexible thermoelectric devices are presented. The hybrid networks were fabricated by direct deposition of thermoelectric material (Bi2Se3, Sb2Te3) on the MWCNT networks using physical vapor deposition technique. Growth mechanisms of Bi2Se3 and Sb2Te3 on MWCNTs were investigated. The Seebeck coefficient and charge transport properties of MWCNT-Bi2Se3 and MWCNT-Sb2Te3 hybrid networks were studied as function of MWCNT wt% in the networks. Variable-range hopping models were applied for the interpretation of conductance mechanisms in the hybrid networks. The Seebeck coefficients of the MWCNT-Sb2Te3 and MWCNT-Bi2Se3 hybrid networks with low MWCNT wt% were found to be comparable with the Seebeck coefficients of pure inorganic Sb2Te3 and Bi2Se3 thin films. At the same time, flexibility tests of the MWCNT-Sb2Te3 and MWCNT-Bi2Se3 hybrid networks with MWCNT 50% showed no significant increase in the resistance when they were bent to a radius of 5 mm. This makes hybrid networks, presented in this work, the perspective for applications in flexible thermoelectrics as thermoelectric coatings for flexible substrates and fillers for polymers-based composites.