Measuring temperature and heat flux is important for regulating any physical, chemical, and biological processes. Traditional thermopiles can provide accurate and stable temperature reading but they are based on brittle inorganic materials with low Seebeck coefficient, and are difficult to manufacture over large areas. Recently, polymer electrolytes have been proposed for thermoelectric applications because of their giant ionic Seebeck coefficient, high flexibility and ease of manufacturing. However, the materials reported to date have positive Seebeck coefficients, hampering the design of ultra-sensitive ionic thermopiles. Here we report an “ambipolar” ionic polymer gel with giant negative ionic Seebeck coefficient. The latter can be tuned from negative to positive by adjusting the gel composition. We show that the ion-polymer matrix interaction is crucial to control the sign and magnitude of the ionic Seebeck coefficient. The ambipolar gel can be easily screen printed, enabling large-area device manufacturing at low cost.

New electrically conducting and mechanically robust fibers and yarns are needed as building blocks for emerging textile devices. In this work, we describe a continuous wet-spinning process for the fabrication of poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) fibers with high electrical conductivity, excellent mechanical properties, and moderate thermoelectric performance by including a drawing stage in dimethyl sulfoxide. Drawing the fibers induced preferential orientation of the polymer chains in the fiber axis direction. With increased drawing, the room temperature electrical conductivity saturated at approximately 2000 S cm–1. The Seebeck coefficient was found to be rather constant with drawing. Therefore, the thermoelectric power factor saturated with applied draw between 40 and 50 μW m–1 K–2. The thermal conductivities of the drawn fibers were measured between 4 and 5 W m–1 K–1 at liquid nitrogen temperatures. Although the relatively high thermal conductivity negatively affects the ultimate thermoelectric performance, it can be beneficial for other applications such as in electrical interconnections. Additionally, at high draw ratios, the Young’s moduli saturated at near 15.5 GPa with maximum break stresses of 425 MPa. To the best of our knowledge, this Young’s modulus is the highest reported for a PEDOT:PSS material. Further, we investigated the degree of preferred orientation by wide-angle X-ray scattering and found a strong correlation between the orientation of the polymer chains along the fiber axis and the trends observed in the fibers’ properties. In general, the fibers with the highest orientation were also the stiffest and the most conducting fibers. We believe these are important steps toward the continuous fabrication of high performance PEDOT:PSS fibers to be used as building blocks in the emerging field of electronic textiles.

NFC–PSSNa composite paper combines high ionic conductivity, high ionic Seebeck coefficient and low thermal conductivity, resulting in an overall slightly better figure-of-merit than PSSNa.

A free‐standing high‐output power density polymeric thermoelectric (TE) device is realized based on a highly conductive (≈2500 S cm−1) structure‐ordered poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate film (denoted as FS‐PEDOT:PSS) with a Seebeck coefficient of 20.6 µV K−1, an in‐plane thermal conductivity of 0.64 W m−1 K−1, and a peak power factor of 107 µW K−2 m−1 at room temperature. Under a small temperature gradient of 29 K, the TE device demonstrates a maximum output power density of 99 ± 18.7 µW cm−2, which is the highest value achieved in pristine PEDOT:PSS based TE devices. In addition, a fivefold output power is demonstrated by series connecting five devices into a flexible thermoelectric module. The simplicity of assembling the films into flexible thermoelectric modules, the low out‐of‐plane thermal conductivity of 0.27 W m−1 K−1, and free‐standing feature indicates the potential to integrate the FS‐PEDOT:PSS TE modules with textiles to power wearable electronics by harvesting human body's heat. In addition to the high power factor, the high thermal stability of the FS‐PEDOT:PSS films up to 250 °C is confirmed by in situ temperature‐dependent X‐ray diffraction and grazing incident wide angle X‐ray scattering, which makes the FS‐PEDOT:PSS films promising candidates for thermoelectric applications.