In-situ synthesis of flexible hybrid composite films for improved thermoelectric performance

Abstract

Thermoelectric (TE) materials and devices, which enable direct conversion of thermal energy into electricity and vice versa, are a favorable technology for waste heat recovery and flexible energy generators and coolers. Here, we report the enhanced thermoelectric properties of flexible hybrid films composed of carbon nanotubes (CNTs) with good electrical and mechanical properties and inorganic nanowires with high Seebeck coefficient synthesized through an in-situ facile solution method. A two-step interface engineering process is applied to the flexible composite aiming to enhance thermoelectric properties: (1) Bi2Te3 nanowires are grown from the surface of uniformly dispersed CNTs by in-situ synthesis, and (2) a mechanical pressing and a post heat-treatment were employed to form tight interface bonding and adjust the nanowires close to stoichiometric composition. Impressively, the CNTs/Bi2Te3 nanowires composite films exhibited a peak TE power factor of approximately 0.74 mW m−1K−2 at room temperature along with admirable flexibility. The Seebeck coefficient and electrical conductivity were improved by a factor of 30 and 2.2, respectively, through mechanical pressing and post-annealing. This increase is attributed to the phase homogenization of inorganic nanowires to its stoichiometric phase and electron filtering effects due to enhanced interfaces both qualitatively and quantitatively. The flexibility and retention of the conductivity were evaluated via two different methods. This composite with high TE performance will be utilized to create flexible thermoelectric devices for energy harvesting. In addition, the findings from this study can be applied to other flexible thermoelectric materials systems to enhance thermoelectric properties.