A Design of Experiments Study on Inkjet-Printed PEDOT:PSS Temperature Sensors

This work presents an approach to develop, study, and optimize the performance of flexible temperature sensors. With the development of Industry 4.0 and the smartification of control processes, there is a high demand for inexpensive, flexible, and seamless sensors that can be adapted to various applications. Concerning the development of flexible printed temperature sensors, the most frequently used materials include silver, carbon allotropes, and polymers, such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). PEDOT:PSS presents great electrical properties, optical transparency, and is inkjet printing compatible. Unfortunately, most PEDOT:PSS and PEDOT:PSS-based composite temperature sensors still lack sensitivity and do not present linear behavior, which challenges their use and reliability. Hence, in this work, different designs of inkjet-printed PEDOT:PSS sensors were studied to determine if their performance could be improved by modifying their layout. The effects of the number of printed layers and printing orientation were also evaluated. The same study was repeated for encapsulated and nonencapsulated sensors. The thermal response of the sensors was studied throughout heating–cooling cycles from 25 °C to 60 °C, and by changing the design, it was possible to improve the sensitivity by 40%, decrease cycle offset by about 60%, and increase linearity for ${R}^{{2}}$ values close to 1. Design and width of printed layers were uncovered as the more impacting factors for these results. The flexibility of the sensors was demonstrated as well, ensuring their functionality under bending.