INSIGHT INTO THE ELECTRONIC PROPERTIES OF ORGANIC SEMICONDUCTORS: EXPERIMENTAL MEASURES FROM THE ISOLATED-MOLECULE LEVEL TO THE SOLID-STATE DEVICE LIMIT

Abstract

Fundamental understanding of the electronic properties, and charge transfer mechanism of organic semiconductors and functionalized oligoacenes in particular, is of great importance for the design and fabrication of organic electronic devices. This work is devoted to the study of the electronic properties of organic semiconductors in the gas, solution, and solid phases, thus providing insights into the intra- and intermolecular electronic interactions of these materials from the isolated-molecule level to the solid-state device limit. The organic semiconductors investigated in this work are bis-triisopropylsilylethynyl-substituted (TIPS) anthracene, TIPS tetracene, TIPS pentacene, bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]-pentacene (TP-5), and 2,2,10,10-tetraethyl-6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]pentacene (EtTP-5). This research is conducted on the basis of experimental and computational studies. The experimental analysis is based on the combination of closely-related gas-phase and solid-phase photoelectron spectroscopy measurements, along with electrochemical measurements in solution. The electronic structure quantum-mechanical computations are performed at the density functional theory level, and are in good agreement with experimental results.This dissertation reports important findings on the electronic properties of organic semiconductors and how these properties change between phases. The role of polarization effects on the electronic properties of these materials was demonstrated to be significant and strongly dependant on the molecular structure and electronic interactions at the isolated- (or single-) molecule level as well as on the molecular packing and electronic interactions in the solid state at the device limit.