Thermoelectric (TE) materials are important for the sustainable development because they enable the direct harvesting of low‐quality heat into electricity. Among them, conducting polymers have attracted great attention arising from their advantages, such as flexibility, nontoxicity, easy availability, and intrinsically low thermal conductivity. In this work, a novel and facile method is reported to significantly enhance the TE property of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films through sequential post‐treatments with common acids and bases. Compared with the as‐prepared PEDOT:PSS, both the Seebeck coefficients and electrical conductivities can be remarkably enhanced after the treatments. The oxidation level, which significantly impacts the TE property of the PEDOT:PSS films, can also be well tuned by controlling the experimental conditions during the base treatment. The optimal PEDOT:PSS films can have a Seebeck coefficient of 39.2 µV K−1 and a conductivity of 2170 S cm−1 at room temperature, and the corresponding power factor is 334 µW (m−1 K−2). The enhancement in the TE properties is attributed to the synergetic effect of high charge mobility by the acid treatment and the optimal oxidation level tuned by the base treatment.

Thermoelectric materials can be used to harvest low‐grade heat that is otherwise dissipated to the environment. But the conventional thermoelectric materials that are semiconductors or semimetals, usually exhibit a Seebeck coefficient of much less than 1 mV K−1. They are expensive and consist of toxic elements as well. Here, it is demonstrated environmental benign flexible quasi‐solid state ionogels with giant Seebeck coefficient and ultrahigh thermoelectric properties. The ionogels made of ionic liquids and poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) can exhibit a giant Seebeck coefficient up to 26.1 mV K−1, the highest for electronic and ionic conductors. In addition, they have a high ionic conductivity of 6.7 mS cm−1 and a low thermal conductivity of 0.176 W m−1 K−1. Their thermoelectric figure of merit (ZT) is thus 0.75. The giant Seebeck coefficient is related to the ion‐dipole interaction between PVDF‐HFP and ionic liquids. Their application in ionic thermoelectric capacitors is also demonstrated for the conversion of intermittent heat into electricity. They are especially important to harvest the low‐grade thermal energy that is abundant on earth.

Nowadays, organic thermoelectric (TE) materials have attracted considerable attention due to their unique merits, e.g., light‐weight, high mechanical flexibility, nontoxicity, easy availability, and intrinsically low thermal conductivity. Among the organic/polymer TE materials reported so far, poly(3,4‐ethylenedioxythiophene):poly(styrenensulfonate) (PEDOT:PSS) is extensively investigated because it is water‐processable, thermally stable, and can be highly conductive. Over the past few years, the TE properties of the PEDOT‐based TE materials are continuously improved. With rational design, some PEDOT:PSS‐based materials have achieved high ZT values comparable to the conventional inorganic TE materials like bismuth telluride at room temperature. This paper reviews the recent breakthroughs for PEDOT:PSS‐based TE polymers and composites. The strategies for achieving high‐performance PEDOT:PSS‐based TE materials and the corresponding underlying mechanism are specifically discussed. The TE devices fabricated by the PEDOT:PSS‐based TE materials are also presented, in terms of their fabrication/assembly technique, device configuration and device performance. With all the exciting progress made in the PEDOT:PSS‐based TE materials, the further development and practical applications of the high‐efficient organic TE materials as flexible TE module devices and wearable electronics can be greatly anticipated.

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Thermoelectric materials can be used as the active materials in thermoelectric generators and as Peltier coolers for direct energy conversion between heat and electricity. Apart from inorganic thermoelectric materials, thermoelectric polymers have been receiving great attention due to their unique advantages including low cost, high mechanical flexibility, light weight, low or no toxicity, and intrinsically low thermal conductivity. The power factor of thermoelectric polymers has been continuously rising, and the highest ZT value is more than 0.25 at room temperature. The power factor can be further improved by forming composites with nanomaterials. This article provides a review of recent developments on thermoelectric polymers and polymer composites. It focuses on the relationship between thermoelectric properties and the materials structure, including chemical structure, microstructure, dopants, and doping levels. Their thermoelectric properties can be further improved to be comparable to inorganic counterparts in the near future.

PSS and the conformation change of PEDOT chains as a result of the synergetic effects of inorganic salts and DMF.

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