High-performance multifunctional piezoresistive/piezoelectric pressure sensor with thermochromic function for wearable monitoring

To meet the application of the pressure sensors in various conditions, a high-performance piezoresistive/piezoelectric (IOF) sensor with a thermochromic function has been designed and fabricated in this work, which consists of a color-changing piezoelectric film (BP) and a piezoresistive layer (FPM) laminated together. Benefiting from the reaction between the color-former and the developer in a temperature-dependent co-solvent, the thermochromic function in the IOF sensor can be achieved, showing from blue at 30 °C to white at 150 °C. Moreover, by introducing Bi0.5Na0.5TiO3 (BNT) piezoelectric material, the BP piezoelectric layer can provide 80 V output voltage, 1.398 V·kPa−1 sensitivity, and 30 ms response time, respectively. Electrical conductivity is imparted to the fabric through the introduction of MXene, and the FPM piezoresistive layer displays 0.835 kPa−1 sensitivity and 73 ms response time in a wide stress range of 0–300 kPa, respectively. When the IOF sensor is attracted to the human body and KN95 masks, it has good sensitivity to measure human behavior, breath airflow, and daily speaking signals, showing a promise to use in wearable monitoring. Summarily, the studied pressure sensor integrates the advantages of piezoresistive and piezoelectric sensors and may provide a new paradigm to develop multifunctional pressure sensors for wearable monitoring with temperature visualization.