A Printable Humidity Sensing Material Based on Conductive Polymer and Nanoparticles Composites

Abstract

To monitor humidity, the polymer-based humidity sensing material has become an emerging candidate because of its low-cost and low-power characteristics. To implement polymer sensing materials, however, the fabrication capability and stability are major concerns. In this work, an inkjet printable humidity sensing material, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), is developed to improve the fabrication capability. Besides, different kinds of nanoparticles, SiO2 and aluminum zinc oxide (AZO), are also employed to enhance the stability and sensitivity to humidity sensing. Based on experimental results, the sensitivity can be improved by 100%; the stability can also be noticeably enhanced. To understand the sensing mechanism, X-ray diffraction (XRD), Fourier transforms infrared diffraction (FTIR), and photoluminescence (PL) spectrometer measurements are performed. Based on these material investigations, the sensing enhancement is due to physical adsorption of the blending nanoparticles. This work proposes a high sensitivity and low cost humidity sensing material for different applications.

PEDOT:PSS/QCM-based multimodal humidity and pressure sensor

“…The complex behavior of traditional resistive PEDOT:PSS-based RH sensors at relative humidity above 60% typically restricts RH sensor operation to either low, mid-range, or high RH regimes 24,[28][29][30] . The unique feature of the RH sensor reported here is that it relies on two inputs.…”

“…Diffusion of H 2 O into PEDOT:PSS films causes film swelling due to protonation of SO 3 H + groups at the PEDOT-PSS interface, resulting in the formation of H 3 O + PSS(SO 3 ) -. Swelling of the film increases the distance between adjacent PEDOT domains, leading to a decrease in charge carrier mobility 24,28,29 . Hydrogen bonding between adsorbed H 2 O and vaporphase H 2 O accelerates H 2 O sorption and leads to further film swelling.…”

“…H 2 O sorption disrupts hydrogen bonding between PSS molecules, leading to changes in viscosity and shear modulus of the polymer matrix (see Supporting Information). The electrical resistivity of PEDOT:PSS increases linearly as RH increases (RH<60%) 28 . At higher values of RH (>60%), a water meniscus is formed on the PEDOT:PSS surface resulting in highly non-linear sensor response over a broad range of humidities 1,3,30 .…”

A Low-Power Integrated Humidity CMOS Sensor by Printing-on-Chip Technology

“…The aqueous nature of PEDOT:PSS also is a good feature for the printing process. To demonstrate the discrimination of different sensing materials toward different gases, aluminum doped zinc oxide (AZO) nanoparticles were added into PEDOT:PSS to form a composite sensing material, which was verified in previous works [24,25]. Pristine PEDOT:PSS and blended PEDOT:PSS/AZO were printed onto the gold electrodes of CMOS chips by a self-made inkjet printing system.…”

Humidity Sensor Based on PEDOT:PSS and Zinc Stannate Nano-composite

“…A resistivity-based PEDOT:PSS humidity sensor 17 was analyzed for humidity sensing below 80% RH. To enhance the sensitivity of PEDOT:PSS, nanoparticles like SiO 2 and aluminum zinc oxide (AZO) have been introduced into the polymer to form nano-composites, 18 but the limitation of the linear response range (20-60% RH) remains an issue which needs to be resolved. The response time of PEDOT:PSS based humidity sensor was highly improved ($1 s) by adding iron oxide nanoparticles, 4 keeping the humidity sensing range for linear response still limited to .…”