(622d) Solvent Extraction and Size Effects On the Electrical and Optical Properties of P3HT Nanostructures

Since the introduction of polythiophene-based electronic devices, advances in synthesis procedures have led to dramatic improvements in molecular ordering and device performance for polythiophene systems. While various semiconducting thiophene derivatives have demonstrated higher mobilities, poly(3-hexylthiophene) (P3HT) has proven to be the most widely studied thiophene material. This is largely because of its solubility in common organic solvents and its exceptionally high carrier mobility among soluble materials. The high mobilities observed originate from the fact that the material forms well ordered films in which high degrees of intermolecular π-orbital overlapping is present. P3HT nanostructures fabricated via template wetting have been shown in our lab to have significantly greater mobilities than thin films as well as very different optical properties.

Synthesis of high quality materials is of the utmost importance, as impurities present in the material can have significant, adverse effects on device performance. Impurities in organic electronic materials can act to limit molecular ordering, trap free carriers, cause unintentional doping effects, and accelerate device degradation. The catalytic materials used in the synthesis are often metallic complexes, including activated Zn. This leads to the presence of undesirable metallic and ionic impurities within the synthesized polymer. Purification processes based on various extraction techniques have been developed and utilized to produce P3HT material with very low metallic content and narrow molecular weight distributions.

In this work, the effect of Soxhlet extraction procedures on the production and properties of P3HT-based semiconducting polymer nanotubes via template wetting nanofabrication will be examined. The extraction process is examined in terms of the Flory-Huggins theory. Electronic properties studied using current voltage characteristics of nanotube diode devices along with corresponding charge transport models while Uv-vis spectroscopy was used to examine the optical properties of various fractions. The optical bandgap of the material is compared to the electrochemical bandgap found through cyclic voltammetry experiments. Comparison of the fractions with the as received bulk material is made. This analysis will help to further understand and qualify the directed assembly of polymer nanotubes constructed by template wetting.