Development of highly sensitive relative humidity sensor based on nanoporous PCPDTBT thin film

A novel type of capacitive humidity sensor with surface-type electrode geometry is presented in the present study. The high sensitivity and significantly high bandwidth associated with this planar-type humidity sensor (Al/PCPDTBT/Al) allow the facile and reliable estimation of ambient humidity. The use of a polymer sensing material Poly[2,6-(4,4-bis-(2-ethylhexyl)-4 H-cyclopenta[2,1-b;3,4-b ՛]dithiophene)-alt-4,7(2,1,3-benzothia-diazole)] (PCPDTBT) with hierarchical nanoporous surface morphology and large surface/volume ratio ensures the sensor's stable performance coupled with swift response to ambient humidity changes. Specifically, at a relatively lower frequency bias signal (i.e., 1 kHz), a fairly higher order of humidity sensitivity has been observed, i.e., 415.07 pF/%RH. While, sensitivities at significantly higher AC signal frequencies (i.e., 10 and 100 kHz) have been experimentally determined to be 345.18 pF/%RH and 154.72 pF/%RH, respectively. Likewise, the resistive sensitivity of the humidity sensor has been estimated to be -3624.88 k & OHM;/%RH, -2381.11 k & OHM;/% RH and -1338.14 k & OHM;/%RH, at 1, 10 and 100 kHz test frequencies, respectively. The operating mechanism of the capacitive humidity sensor relies on an increase in the dielectric constant of the PCPDTBT active sensing layer accompanied by the rise in the ambient humidity levels. In addition to enhanced bandwidth and improved capacitive and resistive sensitivity, the mean response & recovery time of the fabricated device have been recorded to be -4 min, 17 s and-8 min, 43 s, respectively.