Highly sensitive BEHP-co-MEH:PPV + Poly(acrylic acid) partial sodium salt based relative humidity sensor

A high performance humidity sensor for environmental and health monitoring has been fabricated using a composite of BEHP-co-MEH:PPV co-polymer and super hydrophilic Poly(acrylic acid) partial sodium salt (PAASS) as the sensing layer. The device was fabricated using all printing methods. Reverse offset printing was used to fabricate silver electrodes on LiNbO3 piezoelectric substrate while spin coating was used to deposit the composite active layer. Four samples with different concentrations of PAASS were fabricated to find out the effect of super hydrophilic material concentration on the performance of the sensors. Physical, chemical, and electrical characterizations were performed for the sensors and their response was recorded for varying humidity levels. The results showed that the response of sensors towards humidity change is very sensitive, quite stable, and can effectively measure low humidity levels with reasonable response and recovery times. The capacitance of the sensors was measured between 0% RH and 80% RH at 1 kHz and 10 kHz test frequencies. The maximum absolute change in capacitance was ∼2750 pF (34 pF per%RH sensitivity) for the sample with maximum concentration of PAAPSS recorded at 1 kHz test frequency. Different composition ratios resulted in different performance parameters, with some of them improved, and the others compromised. The concentrations can be optimized with application specific requirements.