ELECTROLYTE- GATED THIN FILM TRANSISTORS WITH SOLUTION- PROCESSED SEMICONDUCTORS

The work in this thesis is concentrated on studies of improving the functionality of electrolyte- gated thin film transistors with solution- processed semiconductors in order to provide a promising platform in particular for sensor as transducers and introduce sensitizer layer on the top of the devices to improve their response to specific analytes. Calixarenes, a family of organic macrocycles, were used to bind selectively to waterborne cations, making them an attractive sensitizer option for such species. Here, it is found that calixarenes deposited over the surface of semiconductors using the Langmuir trough also show a positive impact on the performance of TFTs in terms of reducing unwanted electrochemical doping, which often competes with field effect. Also, electron- transporting and electrolyte- gated thin film transistors were demonstrated using precursor- route zinc- oxide (ZnO) semiconductors with hydrophobic surface modifications. This avoids the well- known problem of electron trapping in organic semiconductors. ZnO also shows ambipolar behavior when gated by an ionic liquid (IL) at high applied voltages. Moreover, it is found some organic solvents may act as EDL gate media for TFTs, thus establishing a new family of gate media, in addition to the previously known options (water, ILs, solid electrolytes). This ability is a property of the solvent, not the semiconductor, and a criterion is identified to qualify an organic solvent to act as EDL gate medium. The organic nano- wire (NW) morphology is attractive for sensor applications, due to the high surface area of NWs. Here, both p- type and n- type organic NW films were gated by water. NW TFTs of the hole- transporting polymer P3HT, grown via different solution- based routes, showed lower drain currents, but also lower thresholds, compared to conventional P3HT film TFTs. Water- gated electron- transporting organic TFTs were demonstrated using nano- belts of the n- type organic semiconductor BBL. Performance was improved significantly when using an aprotic organic solvent as EDL gate medium for BBL nano- belt films.