Much of our research focuses on the use of semiconductor thin films in electronic devices, particularly thin film transistors (TFTs) and electrolyte-gated transistors (EGTs). Transistors are not only important switching and amplifying elements for electronics, but they are also outstanding platforms for probing fundament conduction properties of materials as a function of continuously tunable charge density. Electrolyte-gated transistors are a class of TFTs that employ gel electrolytes as high capacitance gate insulators; the high capacitance allows both low voltage operation and enormous charge accumulations in the source-drain channels simultaneously. We are developing device architectures and materials for EGTs that improve their performance and increase the chances for practical application. One set of applications lies in chemical and biomolecular sensing, where the low voltage sensitivity and amplification characteristics of EGTs are a major advantage. Another set of applications is in printed electronics, where the device architecture of EGTs facilitates rapid printing of circuits on plastic using roll-to-roll manufacturing methods. Our fundamental work with EGTs includes the first Hall effect mobility measurement in a polymer semiconductor transistor as a function of charge density.
A particularly intriguing and unusual direction is the application of transistor concepts to control or enhance electocatalytic reactions on the surfaces of 2D semiconductor materials (e.g., MoS2, graphene, ZnO, etc). Transistors operate by controlling carrier concentrations in a thin semiconductor channel adjacent to the gate dielectric. If the semiconductor is thin enough, the charge induced by the underlying gate electrode is exposed on the top surface of the semiconductor. We exploit this by coupling the transistor to an electrochemical cell and then employing the exposed ultrathin semiconductor channel as a gate-tunable working electrode. That is, we adjust the Fermi level position in the 2D semiconductor with the back-gate and examine the impact on electrochemical performance. We hope that this electrochemical platform will allow new insight into the role of electron occupation in the semiconductor density of states on electrocatalysis, e.g., the reduction of oxygen to water at thin metal oxide electrodes, or the reduction of H+ to H2 gas on MoS2.
Printed biosensors based on thin-film transistor technology have been developed for detection of toxins like ricin in food.
Transistor-like electrochemical devices have been developed for electrostatic tuning of electrochemical kinetics on back-gated two-dimensional materials.