Investigation and Modeling of the Electrical Bias Stress in Electrolyte-Gated Organic Transistors

Abstract

Electrolyte-gated organic transistors (EGOTs) are emerging as an important tool in advanced biosensing applications. However, their widespread exploitation is still limited by their poor operational stability. In order to understand the causes of this unreliability, the proposed study focuses on the influence of electrical bias stress (EBS) on EGOTs operating in aqueous electrolytes. Poly(3-hexylthiophene) (P3HT)- and poly[3-(5-carboxypentyl)thiophene)] (P3CPT)-based transistors are studied under the application of a bias in the continuous and pulse mode. Combining electrical and spectroscopic characterizations, it is possible to ascribe the performance variation of P3HT devices to backbone rearrangements induced by side chain oxidation, hydration, and interfacial electrochemical doping at the semiconductor/electrolyte interface, while the presence of polar side chains in P3CPT enhances the oxidative degradation of the polymer throughout the bulk of the film. The charge-trapping model based on a stretched exponential is commonly exploited for the description of EBS in solid dielectric organic field-effect transistors (OFETs). The same model is here applied to fit liquid dielectric EGOT behavior. The extracted material parameters are in good agreement with those found in the literature for P3HT-based OFETs. Finally, a novel improvement of the model is proposed to allow reproducing P3CPT data by accounting for its different degradation process.