Device physics of organic electrochemical transistors

Quinacridone is a five-ring hydrogen-bonded molecule analogous in structure and size to the well-known organic semiconductor pentacene. Unlike pentacene, quinacridone has limited intramolecular π-conjugation and becomes highly colored in the solid state due to strong intermolecular electronic coupling. We found that quinacridone shows a field-effect mobility of 0.1 cm2/V·s, comparable to mobilities of pentacene in similarly prepared devices. Photoinduced charge generation in single-layer quinacridone metal-insulator-metal diodes is more than a hundred times more efficient than in pentacene devices. Photoinduced charge transfer from quinacridone to C60 is not effective, as evidenced by measurements in heterojunctions with C60. Hydrogen-bonded organic solids may provide new avenues for organic semiconductor design.

https://espace.library.uq.edu.au/view/UQ:289468/UQ289468_OA.pdf

Intermolecular hydrogen-bonded organic semiconductors—Quinacridone versus pentacene

A method of fabricating an organic field effect transistor (OFET), including forming a source contact, a drain contact, and a gate connection to a channel comprising semiconducting polymers, wherein the gate connection applies a field to the semiconductor polymers across a dielectric layer to modulate conduction along the semiconducting polymers between the source contact and the drain contact; and treating the semiconducting polymers, wherein the treating includes a chemical treatment that controls a carrier density, carrier mobility, threshold voltage, and/or contact resistance of the OFET.

Doping-induced carrier density modulation in polymer field-effect transistors

The electrical characteristics of molecular tunnel junctions are normally determined by DC methods. Using these methods it is difficult to discriminate the contribution of each component of the junctions, e.g., the molecule-electrode contacts, protective layer (if present), or the SAM, to the electrical characteristics of the junctions. Here we show that frequency-dependent AC measurements, impedance spectroscopy, make it possible to separate the contribution of each component from each other. We studied junctions that consist of self-assembled monolayers (SAMs) of n-alkanethiolates (S(CH2)(n-1)CH3 ≡ SC(n) with n = 8, 10, 12, or 14) of the form Ag(TS)-SC(n)//GaO(x)/EGaIn (a protective thin (~0.7 nm) layer of GaO(x) forms spontaneously on the surface of EGaIn). The impedance data were fitted to an equivalent circuit consisting of a series resistor (R(S), which includes the SAM-electrode contact resistance), the capacitance of the SAM (C(SAM)), and the resistance of the SAM (R(SAM)). A plot of R(SAM) vs n(C) yielded a tunneling decay constant β of 1.03 ± 0.04 n(C)(-1), which is similar to values determined by DC methods. The value of C(SAM) is similar to previously reported values, and R(S) (2.9-3.6 × 10(-2) Ω·cm(2)) is dominated by the SAM-top contact resistance (and not by the conductive layer of GaO(x)) and independent of n(C). Using the values of R(SAM), we estimated the resistance per molecule r as a function of n(C), which are similar to values obtained by single molecule experiments. Thus, impedance measurements give detailed information regarding the electrical characteristics of the individual components of SAM-based junctions.

Equivalent Circuits of a Self-Assembled Monolayer-Based Tunnel Junction Determined by Impedance Spectroscopy

This work was from King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under award nos. OSR-2018-CARF/CCF-3079 and OSR-2019-CRG8-4095.3. F.A. acknowledges the support from The Wilkinson Charitable Foundation. C.M. acknowledges financial support from the Swedish Research Council (grant no. 2018-03824) and the Knut and Alice Wallenberg Foundation through a Wallenberg Academy Fellowship Prolongation grant.

Doping Approaches for Organic Semiconductors

The equivalent circuit parameters for a pentacene organic field-effect transistor are determined from low frequency impedance measurements in the dark as well as under light illumination. The source-drain channel impedance parameters are obtained from Bode plot analysis and the deviations at low frequency are mainly due to the contact impedance. The charge accumulation at organic semiconductor–metal interface and dielectric–semiconductor interface is monitored from the response to light as an additional parameter to find out the contributions arising from photovoltaic and photoconductive effects. The shift in threshold voltage is due to the accumulation of photogenerated carriers under source-drain electrodes and at dielectric–semiconductor interface, and also this dominates the carrier transport. The charge carrier trapping at various interfaces and in the semiconductor is estimated from the dc and ac impedance measurements under illumination.

Interfaces and traps in pentacene field-effect transistor

Electrochemical doping for lowering contact barriers in organic field effect transistors

A numerically efficient method of modeling interdigitated electrodes for capacitive film sensing

In the present contribution femur (leg bone) tissue excised from calves was investigated in vitro by electrical impedance spectroscopy in a frequency range of 40Hz-40MHz. Three different equivalent electrical circuits were tested for suitable representation of the measured data, where the fitting was performed by a complex nonlinear least-square algorithm. Finally, a depth profile of a bone sample is discussed.

Position-dependent characterization of bone tissue with electrical impedance spectroscopy

Interdigitated electrodes represent a commonly used planar structure when it comes to implementing capacitive sensors. The calculation of the created electric fields, however, is very complicated as soon as cover layers are involved. We present a simple semi-analytical approach, which yields approximate expressions for the capacitance between the electrodes. The method can be easily adapted to geometries with multiple cover layers. As an example, the sensitivity of the capacitance to changes in the permittivity for alternate wiring schemes of electrodes is discussed.

Stefan Schaur

Papers

Interfaces and traps in pentacene field-effect transistor

Electrochemical doping for lowering contact barriers in organic field effect transistors

A numerically efficient method of modeling interdigitated electrodes for capacitive film sensing

Position-dependent characterization of bone tissue with electrical impedance spectroscopy

An efficient method for modeling planar interdigitated electrodes for capacitive sensing