Flexo-green Polypyrrole – Silver nanocomposite films for thermoelectric power generation

Abstract

Conducting polymers offer various advantages over inorganic thermoelectric materials such as eco-friendliness, a reduced manufacturing cost, flexibility, low thermal conductivity and amenability to tuning of electrical properties through doping; have recently drawn much attention for conversion of low temperature waste heat (≤150°C) into electricity. In this study, we investigated the thermoelectric properties of hybrid films of polypyrrole and silver (PPy-Ag). These films were prepared on biaxially oriented polyethylene terephthalate (BOPET) flexible substrates by eco-friendly one pot photo-polymerization method using aqueous solution of silver nitrate (AgNO3) as photo initiator. Detailed characterization of the samples revealed that morphology of composite films reorganized with the change in AgNO3 concentration during synthesis. Increasing AgNO3 concentrations resulted in PPy films containing Ag nanoparticles, nanoclusters as well as macroclusters. With alteration in concentration and size of Ag particles in PPy matrix, it has been observed that the electrical conductivity of the films increased (1.5–17.3Scm−1), thermal conductivity decreased (0.16–0.002Wm−1K−1), while Seebeck coefficient moderately reduced from 10.9μV/K to 5.8μV/K. Nearly same doping (N+/N∼0.35) content, improved conjugation length and incorporation of Ag between the PPy chains resulted in improved charge carrier mobility/electrical conductivity in the PPy–Ag films. It is proposed that the interface of Ag and PPy served as scattering sites for phonons, thus leading to reduction of thermal conductivity. This synergetic combination of high electrical conductivity, extremely low thermal conductivity along with moderate Seebeck coefficient in the PPy-Ag films resulted in the highest figure-of-merit of ∼7.4×10−3 at 335K among reported PPy based materials. A prototype thermoelectric power generator was fabricated by integrating six numbers of PPy-Ag films. The fabricated device exhibited maximum voltage and power respectively as 6mV and ∼30pW. The present work opens new avenues for the thermoelectric applications of rarely explored flexible PPy-Ag films prepared by a simple nature-friendly photo-chemical process at room temperature.