Inkjet-printed, flexible, and photoactive thin film strain sensors

In an effort to improve the resilience and reliability of infrastructure systems, many advanced sensors have been developed for structural health monitoring. However, these sensors often suffer from high energy demand, large form factors, and have difficulties conforming to complex structural surfaces. Recently, a self-sensing poly(3-hexylthiophene)–based thin film sensor was proposed, and it was shown that light illumination generates an electrical current that was also proportional to applied strains. However, its strain sensing range was limited largely due to the brittleness of the electrodes. In this study, inkjet printing was employed for printing flexible polymer electrodes that enhanced fabrication scalability and its strain sensing range. First, a commercial off-the-shelf Canon inkjet printer was customized for electrode fabrication. Second, a conductive ink solution was prepared for printing the conductive and transparent thin film electrodes. Then, the printed thin film electrodes were characterized for their electrical conductivity, optical transmittance, profile (i.e. roughness and thickness), and piezoresistivity. Finally, poly(3-hexylthiophene)–based strain sensors were fabricated using these electrodes, and strain sensing was validated to 2% tensile strains.