High-performance humidity sensor based on Schiff base compound with fast response, high sensitivity, and stability for humidity sensing application

In this study, the Schiff base compound, 2-((2,4-dichlorophenylimino)methyl)-5-(diethylamino)phenol (hereafter L2 compound), synthesis has been carried out and then implemented to fabricate three different humidity sensors with different concentrations of L2 compound i.e. 3 wt%, 6 wt%, and 9 wt%. These sensors were checked at altered levels of humidity and at various frequencies. The surface morphologies of the L2 compound with different concentrations are shown in the SEM images. Filled and empty grooves, voids, solid flakes, and flowery structures can be seen in SEM images, which played a sumptuous role in the accommodation of H 2 O molecules and the sensing mechanism. The phototropic mobility is based on the Grotthuss mechanism. When the humidity level was increased from 32 %RH to 96 %RH, the capacitance of the sensor was enhanced from 9.5 pF to 16.7 pF, from 8.95 pF to 11.3 pF, and from 8.7 pF to 10.6 pF at different frequencies of 500 Hz and 10 kHz, and 1 MHz, correspondingly. The response/recovery time of the sensor was 1.7/2.62 s which are better than the reported results. The goodness of fit (R 2 values) 0.87 and 0.96 were noted for the chemisorbed and multi-physisorbed layers and were near to unity and hence considered as the best linear fit. The sensitivity of the sensors was high at 500 Hz. The L2-based sensor's high sensitivity, rapid response/recovery time, and reliable performance make it a good choice for real-time humidity monitoring in environmental control, healthcare, food storage, and industrial applications.