https://doi.org/10.1021/acsaelm.9b00322

This work presents a flexible lightweight bilayer film (polycarbonate/polycrystalline layer of crystalline (BEDT-TTF)xBr-(H2O)y salts [BEDT-TTF = bis (ethylendithio)tetrathiafulvalene] as a promising material for humidity sensing which may be applied in a number of monitoring scenarios. The humidity testing of the bilayer film showed that it is capable of monitoring relative humidity levels from 15 % up to 90 % with a well-defined and reproducible electrical signal. Electrical resistance measurements revealed that the crystalline conducting layer can absorb moisture reaching equilibrium at constant relative humidity as reflected in a stable relative resistance response. Humidity uptake is translated into a fully reversible swelling of the polycrystalline layer of molecular conductor exhibiting a relative change of resistance following a clear exponential dependence inducing the reversible metal/nonmetal structural phase transition. An overview of mechanical and humidity sensing properties of the developed bilayer film corroborates that it can be used as flexible hygrometer as well as moisture sensing units on the board of low-cost electronic sensing devices.

On the Sensing Mechanisms of a Hydroresistive Flexible Film Based on an Organic Molecular Metal