Electronic and sensing properties of polythiophene devices

Polythiophene polymers are promising sensor materials for volatile organic compound (VOC) detection and discrimination. The conductivity in these materials changes upon exposure to VOC vapors. This thesis studies the electronic and sensing properties of various polythiophene polymer based electronic devices. Basic molecular calculations were performed to study the electronic structure of polythiophene molecule at both the neutral and ionized state. Polythiophene organic thin-film transistors (OTFTs) were designed and fabricated. Electrical characterization was carried out at various temperatures to understand the charge transport mechanisms and noise characteristics in these ordered polythiophene thin films. Chemical responses of polythiophene OTFTs to various VOC vapors were tested. The sign and amplitude of the response was found to be dependent upon many parameters, such as polymer molecule structure, polymer film nanostructure, analyte chemical and electrical properties, sensor device structure, and sensor operation conditions. Multiple sensing mechanisms of polythiophene sensors are proposed based on the chemical test results and the understanding of charge transport. Low cost electronic nose devices based on multiple polythiophene polymers ink jetted on single chip devices were fabricated and tested. The results prove the feasibility of using these materials for discrimination of VOCs.