Enhanced Thermoelectric Performance in Hybrid Inorganic-Organic Conducting Polymer Systems

Wearable technologies such as smart watches, smart glasses or even smart pacemakers have caused a paradigm shift in consumer electronics with huge potential in areas such as healthcare, fashion and entertainment (e.g. augmented reality glasses). Currently these devices are still powered by batteries needing frequent replacement or recharging, a key challenge holding back wearable electronics. Thermoelectric generators (TEGs) can provide a potential solution as a wearable power source: they can convert heat into electricity, are safe, long-lasting and maintenance-free with zero-emissions. The Seiko Thermic watch (which generated 60 µW/cm² at DT= 5 K^[1]) and the recently released Matrix PowerWatch are just some examples of how TEG technology has already been implemented in commercial devices. Current TEGs however are plagued by low efficiencies, high manufacturing costs, and are fabricated onto rigid substrates which makes them difficult to integrate into many applications that require conformal installation. To date most thermoelectric (TE) materials under study have been inorganic chalcogenides such as Bi- or Pb-based compounds (e.g. Bi2Te3 and PbTe, ZT ~ 1), intermetallics (e.g. half-Heusler alloys), and clathrates and skutterudites. Interest in organic conducting polymers (OCPs) is rapidly growing due to their mechanical flexibility, low thermal conductivities, elemental abundance, low cost and toxicity as well as solution processability. The TE performance of OCPs however still lags behind that of conventional inorganic TE materials which remain the state of the art for applications near room temperature. Recently hybrid inorganic-organic TE materials composed of inorganic nanostructures and OCPs have emerged as a promising class of flexible high performance TE materials. The TE hybrid materials use the OCPs as the mechanical binder providing flexibility whilst simultaneously contributing to the thermoelectric properties of the composite. This has demonstrated PFs exceeding those of either constituent. The reason for this enhancement is still under debate, however Kumar et al.demonstrated that the enhancement in the PEDOT:PSS–Te(Cux) systemwas dominated by the effects of polymer morphology at the organic–inorganic interface and interfacial charge transfer and not by energy filtering as has previously been assumed. We present the results of an in-depth study on flexible tellurium nanowire-P3HT hybrid systems with significantly enhanced power factors that can be rationalised in terms of the Kang-Snyder model on charge transport.