Analytical Platform To Characterize Dopant Solution Concentrations, Charge Carrier Densities in Films and Interfaces, and Physical Diffusion in Polymers Utilizing Remote Field-Effect Transistors

Abstract

Characterizing doping effects in a conductive polymer and physical diffusion in a passive polymer were performed using a remote-gate field-effect transistor (RG FET) detection system that was able to measure the electrical potential perturbation of a polymer film coupled to the gate of a silicon FET. Poly­(3-hexylthiophene) (P3HT) film doped using various concentrations of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) solutions imposed additional positive potentials on the P3HT RG, resulting in a lower threshold voltage (V th) on the n-channel silicon FET. Changes in V th were related to the induced hole concentrations and hole mobility in P3HT films by using our V th shifting model for the RG FET. We discovered that the electron-donating P3HT and even inorganic materials, indium tin oxide and gold, showed similar electrical potential perturbations dependent on the concentration of F4TCNQ in overlying solutions as the dopant radical anions maximally covered the surfaces. This suggests that there are limited electroactive sites for F4TCNQ binding on electron donor surfaces which results in a similar number of positive charges in film materials forming dipoles with the F4TCNQ radical counteranions. The effect of electron acceptors such as 7,7,8,8-tetracyanoquinodimethane and tetracyanoethylene was compared to that of F4TCNQ in terms of V th shift using our analytical tool, with differences attributed to acceptor size and reduction potential. Meanwhile, this FET analysis tool offered a means of monitoring the physical diffusion of small molecules, exemplified by F4TCNQ, in the passive polymer polystyrene, driven by concentration gradients. The technique allows for nondestructive, nonspectroscopic, ambient characterization of electron donor–acceptor interactions at surfaces.

Oxygen-bearing functionalities enhancing NO2, NH3, and acetone electronic response and response variation by polythiophenes in organic field-effect transistor sensors

“…In a recent publication, 54 we had developed a way to measure changes to the surface potential of the polymer film using a remote-gate field transistor (RG FET) in which the polymer is coupled to the oxide gate of the commercial silicon FET. In another recent study, we used the platform to measure the surface interaction of PTCOOH to understand the unusual high response this polymer had to NO 2 .…”

Suppression of Ionic Doping by Molecular Dopants in Conjugated Polymers for Improving Specificity and Sensitivity in Biosensing Applications

“…Therefore, V th of the RGFET is an independent variable from factors that could alter the impedance of RG modules such as the thickness of the RG materials and SiO 2 and the contact area of media on the RG surface, as shown in our previous work. 23 That is, the RGFET only translates electrochemical potentials at the solution interface to the gate of the Si-FET.…”

“…The Sequential doping method results in smooth morphology of doped PT-COOH films (Figure S6) as was case for F4TCNQ:P3HT films in our previous work. 23 Again, E RG F4TCNQ refers to the electrical potential of a specific RG surface such as SiO 2 , P3HT, and PT(+)-COO − in contact with an F4TCNQ solution dissolved in ACN. A pure SiO 2 surface presents hardly any response to the increased F4TCNQ concentrations ranging from 100 ng/mL to 1 mg/mL (Figure S7) because little or no interaction occurs between F4TCNQ and SiO 2 .…”

Carboxylic Acid‐Functionalized Conjugated Polymer Promoting Diminished Electronic Drift and Amplified Proton Sensitivity of Remote Gates Compared to Nonpolar Surfaces in Aqueous Media

“…Meanwhile, the remote-gate FET (RGFET), in which a sensitive surface is integrated with a commercial Si-FET (Figure 1), only translates the surface potential ( of RG material to the gate of the Si-FET [17] due to the high input impedance of the Si-FET (Figure S1). Thus, the RGFET is advantageous for the investigations of solution interfaces as a function of dipole moments and specific surface responses to the dipole moments.…”

“…Our findings are summarized by plotting the (Figure 3f ) and (Figure 3g) of each RG surface in pH7 water. RGFET mostly translated the interface potentials [17] . Similar values for non-conductive surfaces indicated similar after drift once initially unstable solvent dipole orientations were equilibrated (Figure 3g).…”