CAREER: The Working Mechanics of Organic Electrochemical Transistors

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AbstractNontechnical:The organic electrochemical transistor (OECT) is one of the most successful organic bio-electronic devices. The list of applications of OECTs ranges from sensors for biomolecules, to electrocardiographic recordings, and in-vivo recording of brain activity. Overall, OECTs will open new ways to study and monitor common diseases, which can lead to an improvement of the health and quality of life of people in the US and around the world.However, despite the intense interest in OECTs, the understanding of their working mechanism is incomplete. Models used to describe OECTs split the device in two separate parts - one part describing ionic conduction inside the gate electrolyte, and a second part describing the electronic conduction inside the organic semiconductor. This artificial separation between ionic and electronic currents leads to inconsistencies in the description of the device operation, which have to be resolved in order to increase the performance of OECTs. In its research component, the project aims at enhancing the understanding of the working mechanisms of OECTs. A 2D numerical simulation will be implemented and validated. The model will be used to quantify carrier densities and electric fields inside the devices, to understand the origin of current instabilities of OECTs, and to quantitatively describe the sensing mechanism of OECTs.The educational goal of this project is to increase the awareness and knowledge of the nature and ethics of science for students of introductory science courses and high school students. Short graphic novels will be developed that explain the nature of science using anecdotes from the lives of famous researchers as examples. These teaching materials will be used in an inverted physics classroom.Technical:Organic Electrochemical Transistors (OECTs) hold the promise of enabling new bioelectronic applications and of providing new means to study the working mechanisms of biological systems. OECTs rely on a delicate interplay between ionic and electric currents, which, however, is not sufficiently understood. The research goal of this proposal is to close this research gap and to enhance our knowledge in the working mechanisms of OECTs. To reach this aim, the following objectives are pursued: i) To formulate and validate a two-dimensional drift-diffusion model that quantitatively describes OECT behavior; ii) to study the origin of hysteresis and gate bias stress effects in OECTs; and iii) to study and model the sensing mechanism of OECTs.To describe OECT operation, the continuity equations of all involved charge carriers must be solved along with the Poisson equation. A drift-diffusion simulation will be implemented and validated by moving front experiments, impedance spectroscopy of metal-electrolyte-semiconductor junctions, and electric characterization of systematically varied OECTs. A transient model of OECTs will be implemented to explain the origin of hysteresis and gate-bias stress effects in OECTs. Enzymatic reactions are added to the simulation in order to describe the sensing mechanism of OECTs quantitatively.These experiments have the potential to advance the knowledge in the field: i) the steady state distribution of all charge carriers inside the organic semiconductor will be clarified, which is essential to understand the details of OECT operation. ii) Approaches to avoid instabilities found in current OECTs are proposed, which is essential for a later commercialization. iii) A detailed understanding of the sensing mechanism of OECTs is developed. The educational goal of the project is to strengthen introductory physics teaching by developing modules that discuss the nature and ethics of science. In collaboration with the Access and Support for Successful Undergraduate Research Experiences (ASSURE) program, summer projects will be offered to students from minority serving universities to support them in their applications for graduate schools.