Abstract
Conducting polymer of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is frequently used as soft electrode materials in molecular electronics including organic field effect transistor (OFET). In this thesis, we will report on the fabrication of all-solution-processed organic thin film transistors consisted of PEDOT:PSS polymer and a semiconducting material of triethylsilylethynyl anthradithiophene (TESADT). All the relevant interfacial properties between polymer electrodes and TESADT will also be investigated. The issues of particular interest are energy level alignment, thin film morphology and the molecular alignment of TESADT molecules on PEDOT:PSS substrate. The techniques in use include Ultraviolet Photoelectron Spectroscopy (UPS), X-ray Photoelectron Spectroscopy (XPS), Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy and Atomic Force Microscope (AFM). The bottom-contact OFET devices were fabricated, and the average OFET mobility reaches 0.053 cm2V-1S-1, with a threshold voltage at 6.4 V and an on/ off current ratio of 8.3 × 105. The top-contact OFET devices were also fabricated, and the average OFET mobility achieved is 0.035 cm2V-1S-1, with a threshold voltage at 1.6 V and an on/ off current ratio of 2.2 × 105. Comparing these results with the device performances of OFET consisted of Au electrodes, the bottom contact PEDOT:PSS based devices have better performance than Au based devices. A smaller hole injection barrier of 0.48 eV and a better injection efficiency were found for the TESADT/PEDOT:PSS interface which belong to an ohmic contact resulting from the diffusion of TESADT molecules into the structure of PEDOT:PSS. However, a higher hole injection barrier of 0.88 eV and a worse injection efficiency were found for the TESADT/Au interface which belong to a Schottky contact.