Mercury‐Mediated Organic Semiconductor Surface Doping Monitored by Electrolyte‐Gated Field‐Effect Transistors

Abstract

Surface doping allows tuning the electronic structure of semiconductors at near-surface regime and is normally accomplished through the deposition of an ultrathin layer on top or below the host material. Surface doping is particularly appealing in organic field-effect transistors (OFETs) where charge transport takes place at the first monolayers close to the dielectric surface. However, due to fabrication restrictions that OFET architecture imparts, this is extremely challenging. Here, it is demonstrated that mercury cations, Hg 2+ , can be exploited to control doping levels at the top surface of a thin film of a p-type organic semiconductor blended with polystyrene. Electrolyte-or water-gated field-effect transistors, which have its conductive channel at the top surface of the organic thin film, turn out to be a powerful tool for monitoring the process. A positive shift of the threshold voltage is observed in the devices upon Hg 2+ exposure. Remarkably, this interaction has been proved to be specific to Hg 2+ with respect to other divalent cations and sensitive down to nanomolar concentrations. Hence, this work also opens new perspectives for employing organic electronic transducers in portable sensors for the detection of an extremely harmful water pollutant without the need of using specific receptors.

A Solid‐State Aqueous Electrolyte‐Gated Field‐Effect Transistor as a Low‐Voltage Operation Pressure‐Sensitive Platform

“…Bottom-gate (Si/SiO2) bottom-contact (Cr/Au) OFETs based on blends of 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene:polystyrene (diF-TES-ADT:PS, Figure 1a) deposited by bar-assisted meniscus shearing (BAMS), [27,28] a technique compatible with R2R processes, were prepared according to a previously published protocol. [29,30] The devices prepared and measured in ambient conditions exhibited a remarkable p-type field-effect response with a mobility of 0.8 cm 2 /Vs and a threshold voltage (Vth) of -1.5 V (Figure 1b and Figure S1, Supporting Information) in the saturation regime. However, due to the processing of the organic semiconductor (OSC) in ambient conditions, the presence of water traces inside the active film is inevitable, which is translated in a visible hysteresis and a nonlinear dependence of IDS 1/2 versus VGS in the transfer characteristics and a strong VGS-dependent mobility profile of the as-prepared devices (Figure 1b).…”

“…The diF-TES-ADT:PS blend solution was prepared according to a previously published protocol. [29,30] The agarose solutions with various concentrations (0.75 wt.%, 1.5 wt.% and 3 wt.%) were prepared by dissolving the agarose powder into MilliQ water Film deposition and characterization: For the final device fabrication two kinds of substrates (Si/SiO2 and Kapton) were employed in this work to deposit the OSC:PS blend and agarose gel.…”

Recent Advances in Flexible Field‐Effect Transistors toward Wearable Sensors

“…Various kinds of methods have been proposed to guarantee the selectivity of (bio)chemical sensors, which can be generally categorized into nonenzymatic mechanism‐based and specific receptor‐based sensors. Researchers had reported their attempts in increasing the selectivity of sensors, for instance, using the surface doping characteristics between specific cations and semiconductors (Hg 2+ and p‐type OSCs blending with polysterene), [ 229 ] using high‐active‐facet NPs combined with 1D nanofiber/wires, [ 230,231 ] functionalized nanostructured metal oxides as molecular sieving for selective sensing, [ 232 ] modifying receptors on the semiconducting layers, [ 233 ] designing and developing aptamer‐based sensing layers for specific species of (bio)chemical molecules, [ 234,235 ] and integrating bioenzymes into sensing layers to detect biochemical substances. [ 32 ] Reports surrounding the enhancement of FET sensors have been massively put out using surface‐functionalized semiconducting materials to increase the device sensitivity and selectivity.…”

“…[ 32 ] Reports surrounding the enhancement of FET sensors have been massively put out using surface‐functionalized semiconducting materials to increase the device sensitivity and selectivity. [ 229 ] A water‐stable FET chemical sensor was reported using a polyisoindio‐based polymer functionalized with siloxane‐containing solubilizing side chains (PII2T‐Si) as the semiconducting layer to selectively sense the Hg 2+ cations in aqueous solutions. [ 161 ] The PII2T‐Si based FET sensor exhibited stable operation performances in both ambient conditions and aqueous solutions.…”

Nanoscale Mapping of the Conductivity and Interfacial Capacitance of an Electrolyte‐Gated Organic Field‐Effect Transistor under Operation

“…[27] The stability of these EGOFETs could be partly related to the observed ultrathin layer of PS that could act as a capping layer to ion diffusion into the semiconductor. [36] Having access to this information can be specifically useful for the case of biosensors based on organic transistors and to better understand the coupling of excitable cells with these devices for electrical cell recordings. [3] The application of the present approach to other electrolyte gated transistors, including OECTs, requires further study.…”