Highly Conductive Flexible Printed PEDOT:PSS films for Green Humidity Sensing Applications

Abstract

Over the past decades, humidity sensors have been an important sensing component in climate monitoring, agriculture, medical diagnostics and industrial process control systems. With emerging applications such as wearable devices and the internet of things in 5G scenarios, there is a growing demand for accurate humidity measurements, low-cost manufacturing processes for high-volume, high-performance sensors with flexible form factors, and the use of environmentally friendly materials. We present a simple, fast, and cost-effective method for the large-scale fabrication of highly-conductive, all-polymer, and bio-degradable humidity sensors on flexible organic polymer (polyimide) and paper substrates. We investigate the resistive properties of different thicknesses of poly(3,4-ethylenedioxythiophehe) polystyrene sulfonate (PEDOT:PSS) on Kapton and paper substrates in response to humidity, demonstrating a 3—8 Ω/square sheet resistance, suitable for all-polymer circuits. A relative resistance variation of 36.3% at levels of relative humidity ranging from 20% to 80% is demonstrated for a pristine sample, along with 1-month ageing tests to investigate the lifetime of the proposed sensor.