Electric-field-controlled conductance of “metallic” polymers in a transistor structure

Abstract

It was recently reported that use of a doped "metallic" polymer as the active channel in a field effect transistor structure results in unexpected "normally on" transistorlike behavior. We report here the role of ion migration in transistors based on metallic polymer ͓poly͑3,4-ethylenedioxythiophene͒ doped with poly͑styrene sulfonic acid͒ ͑PEDOT:PSS͔͒. The analysis of the ion flow into the active channel due to the gate voltage suggests that for the transistors studied compensating ϳ2 counterions per 100 dopant molecules suppresses PEDOT conductance up to three orders of magnitude. We determine from the temperature dependence of the conductivity of the active channel that the change in conductance of the active channel is throughout the channel in contrast to confinement of gate field induced charge carriers to the channel/dielectric interface in conventional transistors. The decrease of channel conductance reflects an increase of activation energy of carriers. Therefore, we propose that removal of intermediate hopping sites in the disoriented PEDOT:PSS by a small fraction of ion charge compensation causes carriers to anisotropically hop over longer distance leading to a conductor-nonconductor transition.

Electron-ion interaction in doped conducting polymers

“…The experimental dependence is rather smooth with the gate voltage. [17][18][19][20][21] For this reason, we failed to obtain satisfactory fit of the experimental I͑V͒ characteristics using the derived theoretical dependencies, Eqs. ͑36͒-͑39͒.…”

“…We assume also that z i = z e ͉e͉, i.e., we deal with holes and cations as it take place in the experiments. [17][18][19][20][21] From the requirement of electroneutrality ͓Eq. ͑21͔͒, it follows that satisfies the equation…”

“…In Ref. 21, it was proposed that the field effect in conducting polymers is mainly due to the suppression of mobility of primary charge carriers ͑holes͒. Within the granular model, the mobility is determined by the hopping along the chains linking grains.…”

“…More results of experimental study of the doped conducting-polymers based transistors can be found in recent publications. [19][20][21] Because I-V characteristics of the conducting polymerbased transistors are similar to that of semiconductor transistors, the first attempts 20 to describe the observable field effect in the polymer were made by using the known models for conventional semiconductor field effect. However, it leads to unreasonable values of parameters 20 and does not answer the main question of how the electric field penetrates in the polymer conductors with so high concentration of mobile charge carriers.…”

Optimum Design of Organic Electrochemical Type Transistors for Applications in Biochemical Sensing

“…The decrease in conductivity has also been interpreted in terms of an ion-leveraged mechanism, where the disorder driven metal-insulator-transition is characterized by charge localization which is controlled by the ionic environment [8,9]. This model interprets the slow response to the percolation of the ions from the electrolyte into the organic film, under the influence of the vertical electric field, affecting the conductance of PEDOT:PSS [8,9].…”