The development of new flexible and stretchable sensors addresses the demands of upcoming application fields like internet-of-things, soft robotics, and health/structure monitoring. However, finding a reliable and robust power source to operate these devices, particularly in off-the-grid, maintenance-free applications, still poses a great challenge. The exploitation of ubiquitous temperature gradients, as the source of energy, can become a practical solution, since the recent discovery of the outstanding thermoelectric properties of a conductive polymer, poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT:PSS). Unfortunately the use of PEDOT:PSS is currently constrained by its brittleness and limited processability. Herein, PEDOT:PSS is blended with a commercial elastomeric polyurethane (Lycra), to obtain tough and processable self-standing films. A remarkable strainat-break of ≈700% is achieved for blends with 90 wt% Lycra, after ethylene glycol treatment, without affecting the Seebeck voltage. For the first time the viability of these novel blends as stretchable self-powered sensors is demonstrated.

With the emergence of stretchable/wearable devices, functions, such as sensing, energy storage/harvesting, electrical conduction, should ideally be carried out by a single material, while retaining its mechanical properties (e.g. ability...

Dedicated to the memory of Prof. Michael Bendikov and his many contributions to the field of organic electronics

high demand, especially when characterized by flexibility, extensibility, durability, and low costs. Examples of such devices include health monitoring devices, [1] soft robotics, [2] and functional artificial skin. [3] Although the technology has greatly improved since the first modern applications over a century ago, most sensors are still powered by batteries, limiting their reliability and sustainability. In cases like continuous monitoring, off-the-grid, and maintenance-free applications, self-powered sensors would be extremely desirable.Toward this aim, several energy harvesting strategies have been explored, based on triboelectricity, [4] piezoelectricity, [5] pyroelectricity, [6] and others. [7] Among these, thermoelectricity is recognized as a very reliable and durable potential energy harvesting phenomenon for self-powered sensors [8] exploiting temperature gradients found ubiquitously. Since its discovery in the early 1800s, the thermoelectric (TE) effect has been used only in niche applications due to the relative low efficiencies, [9] high processing costs, toxicity, and rarity of some of the elements (e.g., tellurium, bismuth, antimony) currently used in the manufacture of commercial devices. Nevertheless, there has been a recent renewed interest in TE technology due both to the discovery of new materials and to new applications, in conjunction with solar cells, [10] supercapacitors, [11] and gating transistors. [12] Flexible and stretchable electronic devices have a broad range of potential uses, from biomedicine, soft robotics, and health monitoring to the internetof-things. Unfortunately, finding a robust and reliable power source remains challenging, particularly in off-the-grid and maintenance-free applications. A sought-after development overcome this challenge is the development of autonomous, self-powered devices. A potential solution is reported exploiting a promising n-type thermoelectric compound, poly nickel-ethenetetrathiolates (Na x (Ni-ett) n ). Highly stretchable n-type composite films are obtained by combining Na x (Ni-ett) n with commercial polyurethane (Lycra). As high as 50 wt% Na x (Ni-ett) n content composite film can withstand deformations of ≈500% and show conductivities of ≈10 −2 S cm −1 and Seebeck coefficients of approx. −40 µV K −1 . These novel materials can be easily synthesized on a large scale with continuous processes. When subjected to a small temperature difference (<20 °C), the films generate sufficient thermopower to be used for sensing strain (gauge factor ≈20) and visible light (sensitivity factor ≈36% (kW m −2 ) −1 ), independent of humidity (sensitivity factor ≈0.1 (%RH) −1 ). As a proof-of-concept, a wearable self-powered sensor is demonstrated by using n-type Na x (Ni-ett) n /Lycra and PEDOT:PSS/Lycra elements, connected in series by hot pressing, without employing any metal connections, hence preserving good mechanical ductility and ease of processing.