A Highly Sensitive Pyroresistive All‐Organic Infrared Bolometer

Abstract

when processed as thin fi lms. [ 14,15 ] An alternative method to register the surface temperature of an object is a direct-contact measurement using simple paste-on temperature sensors, such as a thermistor or a thermocouple. [ 7 ] These devices provide more accurate temperature values compared to noncontact approaches, but their response time is too slow for the needs in the emerging fi eld of fast temperature sensors. [ 16 ] In this regard, the development of all-organic infrared bolometers able to operate at ambient temperature as contact-less temperature sensors is very appealing because of the intrinsic properties of organic materials. [16][17][18][19] The fi rst organic bolometer made of a thin cellophane foil painted with aquadag has been demonstrated by Niven over 70 years ago. Due to the water solubility of the emploied paint, however, the device exhibited a large moisture dependence and was not stable under ambient conditions. [ 20 ] More recently single walled carbon nanotubes (SWCNT) have been used to prepare sensitive infrared sensors either by embedding such active components in a polymeric matrix [ 21 ] or by using suspended fi lms of SWCNTs. [ 22 ] In this paper, we report bilayer (BL) composite fi lms, [ 15,23,24 ] composed of a polymeric matrix with a top layer formed by a crystalline network of a conducting molecular ion-radical salt (IRS), as materials able to sense, reversibly and fast, very small changes of temperature of objects both in a direct-contact and in a contact-less manner, due to the pyroresistive properties of the molecular conductor and the low mass/heat-capacitance of the composite fi lms. Such BL fi lms have a sensitivity one orderof-magnitude larger than most commonly used metal or metalalloy based temperature sensors, [ 25 ] combining the fl exibility, lightweight, and easy processing properties of polymers. In the fi eld of radiation sensors, voltage-(V/W) or current-responsivity (A/W), given by the ratio between output of the electrical signal and the radiation power, measures the input-output gain of such sensing systems. In this work, the responsivity, which is defi ned as the relative change of resistance upon exposure to optical radiation power was extracted for different wavelengths in the range from 532 to 6960 nm. The resulting responsivity of BL fi lms exhibits only a small variation over the full measurement range, as expected for a bolometer. Moreover, a few proof-of-concept experiments with simple passive infrared sensor prototypes are reported, demonstrating that the developed BL thin fi lms are very attractive as a new generation of durable and low-cost all-organic contact-less temperature sensors with potential applications in areas such as biomedicine, human health care, smart electronic skin, and robotics. Back in 1878, and driven by the scientifi c interest in studying the sun and its effect on weather, Langley invented the bolometer; a radiant-heat detector that is sensitive to extremely small temperature variations. [ 1 ] Since then there has been a tre...

On the Working Mechanisms of Solid‐State Double‐Layer‐Dielectric‐Based Organic Field‐Effect Transistors and Their Implication for Sensors

“…[32,33] In sharp contrast to bolometers, [34] which typically show wavelength independent response and are based on local heating of the sensing element, the operation of photodetectors is based on the photoeffect, [35] inducing electronic transitions to higher energy levels and the generation of mobile charge carriers. Photo detectors based on organic semiconductors have been shown previously.…”

Investigation of sensing capabilities of organic bi-layer thermistor in wearable e-textile and wireless sensing devices

“…1) which can be used both as a direct-contact thermometer and as a passive noncooled infrared sensor [4]. This sensor is capable of identifying even negligible temperature changes with accuracy of 0.005 degree [4]. The obtained results improve those obtained from widely used thermistors: the accuracy of a Pt-1000 detector is 0.01 degree [28].…”

“…It should be noted that one of the important areas for innovation in the field of organic electronics is sensing [2]. For example, it was shown that some of organic molecular conductors, such as trihalides of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), are able to give electronic devices extraordinary strain, pressure and temperature sensing properties impossible to achieve with metal-based electronic structures, enabling a broad range of innovative "out-of-thebox" applications [3,4,5,6]. On the other hand, the attraction of (BEDT-TTF) 2 Hal 3 -organic molecular conductors is the ability to directly impact the sensing properties of the material when deposited in thin film form [3,7].…”

“…It can be successfully combined with plastic films by relying on a low cost simple synthetic procedure described in [24,25]. This procedure shows that conducting bi-layers polycarbonate/(BEDT-TTF) 2 X 3 are highly effective as inexpensive lightweight strain [3], temperature [4] and humidity sensors [26] in terms of their application to a remote patient monitoring. Another significant advantage is integration of the strain sensing polycarbonate/polycrystalline (001) oriented α-(BEDT-TTF) 2 I 3 bi layer film into a polyester textile.…”

“…In our recent work, we have reported on the bi layer film: polycarbonate/polycrystalline (001) oriented α'-(BEDT-TTF) 2 I x Br 3-x molecular conductor [hereafter it will be as polycarbonate/α'-(BEDT-TTF) 2 I x Br 3-x ] ( Fig. 1) which can be used both as a direct-contact thermometer and as a passive noncooled infrared sensor [4]. This sensor is capable of identifying even negligible temperature changes with accuracy of 0.005 degree [4].…”