Thermoelectric polymer materials

The thermoelectric effect is a physical phenomenon that converts electrical energy into a temperature difference (Peltier effect) or, conversely, a temperature difference into electrical energy (Seebeck effect). In addition to the use of thermoelectricity for thermometry and refrigeration, devices exploiting this effect are of interest for recovering heat released or lost on exothermic installations. In the current economic and environmental context, these systems have strong development potential and should make it possible to reduce energy consumption by recovering waste heat, and possibly improve the efficiency of certain devices by limiting the effects of overheating. The development of materials capable of adapting to complex geometries and exploiting small temperature differences could, for example, make it possible to recover human heat or the heat from portable devices in daily use, offering virtually unlimited potential for energy recovery... Polymers for thermoelectricity are being developed in this niche and with this objective in mind, for operating temperatures close to room temperature.

The performance of a thermoelectric material is characterized by its adimensional figure of merit, whose expression is given below:

The ZT figure of merit is therefore the product of the electrical conductivity σ and the Seebeck coefficient α divided by the thermal conductivity κ. A good thermoelectric material must therefore have high electrical conductivity (in the case of metals) and a high Seebeck coefficient, while also being a good thermal insulator (in the case of insulators). The thermoelectric effect is observable in most conducting materials (except for superconductors below T _c ), but the figure of merit is optimal for carrier concentrations characteristic of semiconducting materials. This behavior was first demonstrated for certain inorganic semiconductors, notably bismuth telluride which, with a ZT close to 1, remains the reference material for near-ambient temperature applications. Many other inorganic materials have been studied, such as clathrates, skutterudites, etc., but only perform well at higher operating temperatures.

Following a trend already observed in other fields, such as photovoltaics, transistors, light-emitting diodes, etc., since the early 2000s, the development of organic thermoelectric materials has generated a real craze. In fact, the need to develop systems that can be easily shaped while being...