Abstract

        Conducting polymers and organic molecules are a class of materials which are interesting because of their unusual properties. These materials are lightweight, flexible, easily processed and inexpensive, but conduct electricity. Physicists and chemists worldwide explore these unusual properties and use theses materials to fabricate electronic devices, such as light emitting diodes and transistors. This field was recognized when the 2000 Nobel Prize in chemistry was awarded to A.J. Heeger, A.G, MacDiarmid and Hideki Shirakawa for “the discovery and development of conductive polymers.” This thesis is exploring some of these interesting materials in both theory and experiment.

        For theory, quantum chemical calculations are performed to address the origin of the red shift of the emitted light under forward bias in color-variable alternating-current light emitting (SCALE) devices. We found that the coulomb attraction due to protonation of pyridine rings by sulfonic acid containing polymers causes red shift in the band gap though the steric repulsion after protonation competes with the attraction. Hence we conclude that protonation at polymer-acidic polymer interfaces is responsible for the color variation in SCALE devices.

        For experiment, charge carrier mobilities of two new materials, Tris-[4-(2-{4-[3,6-Bis(4-t-butylphenyl)cabazole-9-yl]phenyl}vinyl)phenyl]amine (TPA-Cz3d) and 9,10-Bis(2-{4-[5-(4-dodecyloxyphenyl)-1,3,4-oxadiazole-2-yl]phenyl}ethynyl) anthracene (ANTH-OXA6t-OC12), under different applied voltages at room temperature (~300K) are measured by the time of flight (TOF) method. The TOF photocurrents are analyzed by both Xiaoming Zou’s model and Scher-Montroll model. We conclude that Scher-Montroll model is not easy to be applied to obtain quantitative values of the mobility. On the other hand, Zou’s model provides a way to obtain the mobility consistently and quantitatively for comparisons of all organic materials. However, this model needs much more experimental data and agreements from some fundamental theory, such as quantum dynamics, to convince people that the mobility obtained by this model is reliable enough for quantitative applications.