CAREER: The interface is the device: Elucidating the role of the contact/organic interface in organic electrochemical transistors

Organic electrochemical transistors (OECTs) are amplifiers with a unique ability to translate biological signals to electron signals in flexible, skin-like electronic materials. The overarching idea behind this research is that addressing the knowledge gap on the interface between the electrode and electronic material will significantly advance OECT sensitivity, energy consumption, reproducibility, reliability and figure of merit analysis, for applications including biosensors, medical and drug delivery devices, body-machine interfaces, adaptive healthcare technologies, neuromorphic hardware and computing, chemical sensors and agricultural applications.

The educational outreach goal of this project describes three activities for disseminating the research from this research, with the potential to reach over 1000 youth and 250 adults overall. The impact envisioned here is distinctively beneficial for teaching students about the challenges in producing fundamental knowledge to advance emerging technologies including, in this case, several that are highly relevant to rural Kentucky; for example, low-cost sensors for agriculture and remote healthcare, including opiate biosensors, could play an integral role in a connected healthcare internet of things for better medical treatment in remote, rural areas in Kentucky.

A workshop to support math and physics classes is proposed as part of a long-term goal to train and motivate Kentucky students to be future scientists. An organic transistor course for K-12 students is proposed to increase exposure to STEM activities. Community engagement activities include a 4 H Teen Conference, supported by a new partnership with Kentucky 4-H.

While transistor performance is dominated by the contact/semiconductor interface, this critical interface is overlooked in OECTs. Present state-of-knowledge is limited and contradictory. Limited knowledge is a problem because the contact/organic interface defines contact resistance, size, speed, power consumption and efficiency, in low-cost, solution-processible OECTs, whose ability to convert biological-to-electronic signals gave rise to organic bioelectronics.

The fundamental roadblock for commercializing OECT technologies, and to fully realizing OECT potential, is the knowledge gap on the mechanistic role of the contact/organic interface. Specifically: (1) The inability to define contact resistance prevents OECT miniaturization, while also increasing OECT energy consumption and reducing their speed. (2) A difference between the channel resistance predicted by the existing model, versus channel resistance as measured in OECTs, means that current is not maximized. (3) Inconsistencies in understanding how device architecture impacts gm results in limited sensitivity.

Therefore, there is a great need to fill the contact/organic interface knowledge gap for OECTs. Here, three objectives have been established to address the specific gaps in knowledge of the OECT contact/organic interface. The first objective is to determine the parameters affecting contact resistance.

The second objective is to elucidate the physical origin of the relationship between contact and channel resistances and operating voltage. The third objective is to identify the inconsistencies in device architecture that cause differences between predicted and measured transconductance. Successful outcome of the proposed research is expected to enable the development of community wide OECT fabrication standards, and guide OECT model development for accurate organic mixed ionic electronic conductor figures of merit analysis.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.