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Organic thermoelectric (TE) materials are regarded as the next‐generation TE materials because of their merits including low cost, high mechanical flexibility, and low intrinsic thermal conductivity. However, their Seebeck coefficient is usually quite low. Herein, a new strategy is demonstrated to greatly enhance the Seebeck coefficient of poly(3,4‐ethylenedioxy‐thiophene):poly(styrenesulfonate) (PEDOT:PSS), which is the most popular TE polymer, through polaron level splitting via π–π overlapping with nonpolar small aromatic molecules including anthracene, naphthalene, and pyrene. Although these aromatic molecules are neither oxidizing nor reducing agent, they can greatly enhance the Seebeck coefficient of PEDOT:PSS films pre‐treated with dimethyl sulfoxide, acid, or acid then base, while they do not lower the electrical conductivity too much. Through such a treatment with anthracene, the Seebeck coefficient can be up to 45.5 µV K−1, and the ZT value can be up to 0.27. The enhancement is ascribed to the splitting of the lower polaron energy level of PEDOT, which is induced by the π–π overlapping between the aromatic compounds and conjugated PEDOT. This can shift up the Fermi level, thereby enhancing the Seebeck coefficient. [ABSTRACT FROM AUTHOR]

Highlights: An ion–electron coupled thermoelectric material was successfully prepared, which theoretically proved the ion–electron thermoelectric synergy effect and this material can work for a long time, which promoted low-grade thermal energy conversion. In the new operating mode of ion–electron thermoelectric synergy effect, our ionic thermoelectrics have a high Seebeck coefficient of 32.7 mV K−1 and a high energy density of 553.9 J m−2, enabling self-power for electronic components. Ionic thermoelectrics (i-TE) possesses great potential in powering distributed electronics because it can generate thermopower up to tens of millivolts per Kelvin. However, as ions cannot enter external circuit, the utilization of i-TE is currently based on capacitive charge/discharge, which results in discontinuous working mode and low energy density. Here, we introduce an ion–electron thermoelectric synergistic (IETS) effect by utilizing an ion–electron conductor. Electrons/holes can drift under the electric field generated by thermodiffusion of ions, thus converting the ionic current into electrical current that can pass through the external circuit. Due to the IETS effect, i-TE is able to operate continuously for over 3000 min. Moreover, our i-TE exhibits a thermopower of 32.7 mV K−1 and an energy density of 553.9 J m−2, which is more than 6.9 times of the highest reported value. Consequently, direct powering of electronics is achieved with i-TE. This work provides a novel strategy for the design of high-performance i-TE materials. [ABSTRACT FROM AUTHOR]

Ionic thermoelectric (i‐TE) materials have attracted much attention due to their ability to generate ionic Seebeck coefficient of tens of millivolts per Kelvin. In this work, we demonstrate that the ionic thermopower can be enhanced by the introduction of multiple ions. The multi‐ionic hydrogel possesses a record thermal‐to‐electrical energy conversion factor (TtoE factor) of 89.6 mV K−1 and an ionic conductivity of 6.8 mS cm−1, which are both better than single salt control hydrogel. Subsequently we build a model to explain thermal diffusion of the ions in multi‐ionic hydrogels. Finally, the possibility of large‐scale integrated applications of multi‐ionic hydrogels is demonstrated. By connecting 7 i‐TEs hydrogels, we obtained an open‐circuit voltage of 1.86 V at ΔT=3 K. Our work provides a new pathway for the design of i‐TEs and low‐grade heat harvesting. [ABSTRACT FROM AUTHOR]

Ionic thermoelectric materials attract widespread attention due to their large Seebeck coefficient compared with electronic thermoelectric counterparts whose main charge carriers are electrons or holes. The present work shows that the ion-polymer matrix interaction can alter the Seebeck coefficient to a great extent. To further shed light on the role of ions, seven water-soluble inorganic chlorides are utilized in this work, to highlight the influence of the cationic softness parameter on the Seebeck coefficient in a PEDOT:PSS ionic conductor. We notice that cations with a positive or a small negative softness parameter value exhibit a negative Seebeck coefficient, resulting from limited thermal diffusion of the cations that are strongly bound to PSS- anions. Conversely, cations with a sufficiently negative softness parameter exhibit fast thermal diffusion due to weak binding to PSS- and, thus, lead to a positive Seebeck coefficient. Based on the established relationship, robust thermoelectric materials with a tunable Seebeck coefficient ranging from –9.63 mV/K to +3.07 mV/K are demonstrated. Our work highlights the important role of ionic properties and provides a pathway for the rational selection of ions in ionic thermoelectrics. [ABSTRACT FROM AUTHOR]

Abstract: 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. [ABSTRACT FROM AUTHOR]

Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a promising thermoelectric (TE) material. Nonetheless, its practical application is hindered by the poor TE properties of the pristine PEDOT:PSS and complicated treatment procedures. Enhancing its electrical conductivity is a key step for the improvement of TE properties. Here, a simple method is introduced to enhance the conductivity by adding sulfonic acid into the PEDOT:PSS solution. A systematic study of representative sulfonic acids with various functional groups suggests that steric effect induced by the functional groups has remarkable impact on the conductivity. The highest conductivity of 1996 S cm−1 is observed in benzenesulfonic acid‐doped PEDOT:PSS films. The doped PEDOT:PSS films are further treated with dimethyl sulfoxide and hydrazine successively or synchronously to tune the oxidation level. A maximum power factor (PF) of 203.1 µW m−1 K−2 is obtained. The high PF of treated PEDOT:PSS allows the realization of a flexible thermoelectric generator, which can generate 4.6 mV thermovoltage when attached on human skin. It also shows a good linear response with the increase of temperature difference; thus, it can be potentially used as a flexible thermal sensor. The facile fabrication process and good TE performance provide PEDOT:PSS an opportunity in wearable electronics. A facile approach to enhance the thermoelectric properties of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) films is reported. Stereo and conjugated structures of the sulfonic acids play a vital role in conductivity enhancement. A high power factor of 203.1 µW m−1 K−2 is achieved with a hydrazine/dimethyl sulfoxide mixed solution treatment. A flexible thermoelectric generator is fabricated and delivers 4.6 mV voltage on human skin. [ABSTRACT FROM AUTHOR]