Graphene-based multifunctional humidity sensors with an ultrahigh current response

Abstract

Prospective composites, based on graphene (G) and hexagonal boron nitride (h-BN) nanoparticles, synthesized using a plasma jet and conducting polymer PEDOT:PSS, were used to create and study a set of sensors in the current study. The composites used were G:PEDOT:PSS (GPP) and G:h-BN:PEDOT:PSS (GBNPP). The PEDOT:PSS content in the composites was 10⁻³ wt%, and the ratio of G : h-BN was 1 : 1 in GBNPP. The development of these new highly conductive graphene-based composites makes it possible to create an active sensor layer with an ultra-low thickness of several nanometers. The ultra-high sensitivity of the current response, S, was ((2.0–3.3) × 10⁶)% for GPP and GBNPP (2–3 printing layers) for a humidity range of 20–80%. The sensor response in the form of current pulses associated with human breathing has a range of ∼2–3 orders of magnitude. Two different processes are assumed to determine the form of the current pulse: the first is a fast process with a rise time of less than 1–4 seconds; the second is a relatively slow process with a front time of several tens of seconds. When touching with a finger (useful, for instance, for a flexible touchpad), a current response was observed as pulses of ∼2–3 orders of magnitude. We hypothesize that skin sweat is likely to play a critical role in the sensory response. Thus, this work presents an effective approach to creating a highly sensitive humidity sensor based on composite 2D materials. Moreover, the ultra-high sensitivity of the studied sensors is accompanied by their low cost and ease of manufacturing by 2D-printing.