Abstract
In this paper, we present a simple, fast, and cost-effective method for the large-scale fabrication of high-sensitivity humidity sensors on flexible substrates. These sensors consist of a micro screen-printed capacitive structure upon which a sensitive layer is deposited. We studied two different structures and three different sensing materials by modifying the concentration of poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) in a graphene oxide (GO) solution. The results show that the aggregation of the PEDOT:PSS to the GO can modify its electrical properties, boosting the performance of the capacitive sensors in terms of both resistive losses and sensitivity to relative humidity (RH) changes. Thus, in an area less than 30 mm2, the GO/PEDOT:PSS-based sensors can achieve a sensitivity much higher (1.22 nF/%RH at 1 kHz) than other similar sensors presented in the literature which, together with their good thermal stability, time response, and performance over bending, demonstrates that the manufacturing approach described in this work paves the way for the mass production of flexible humidity sensors in an inexpensive way.
Highlights
Over the last few years, flexible electronics attracted more and more interest in diverse fields of science and technology
The number of sensing variables, whether environmental or biological, as well as the different ways they can be addressed, resulted in a wide range of studies, among which relative humidity (RH) sensors attracted notable attention given their importance for diverse processes and industries, such as food, biomedicine, and the living environment [3,4,5,6]
Numerous materials have been considered for the manufacturing of flexible RH sensors, such as carbon nanotubes (CNTs) [7], silicon nanosheets (SiNSs) [8], metal–organic frameworks (MOFs) [9], polymers [10], or oxides [11,12]
Summary
Over the last few years, flexible electronics attracted more and more interest in diverse fields of science and technology. It is a rapidly developing field of research boosted by the recent advances in two transversal fields: materials for flexible electronics and the compatible fabrication technologies [1] This interest comes up in response to the challenges imposed by the new electronic applications of the Internet of things (IoT) era, where a trend toward ubiquitous sensing is becoming increasingly clear [2]. PEDOT:PSS is widely used in combination with a large variety of organic materials in order to tune its inherent properties, such as conductivity, dielectric constant, or flexibility [15,16] Following this direction, we present a cost-effective approach for the fabrication of flexible RH sensors using a GO/PEDOT:PSS composite as a sensitive layer.
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