Flexible and Stretchable Self‐Powered Multi‐Sensors Based on the N‐Type Thermoelectric Response of Polyurethane/Na _x (Ni‐ett) _n Composites

Abstract

Flexible and stretchable electronic devices have a broad range of potential uses, from biomedicine, soft robotics, and health monitoring to the internet‐of‐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.