Effect of Molecular Weight on the Structure and Crystallinity of Poly(3-hexylthiophene)

Abstract

Recently, two different groups have reported independently that the mobility of field-effect transistors made from regioregular poly(3-hexylthiophene) (P3HT) increases strongly with molecular weight. Two different models were presented: one proposing carrier trapping at grain boundaries and the second putting emphasis on the conformation and packing of the polymer chains in the thin layers for different molecular weights. Here, we present the results of detailed investigations of powders and thin films of deuterated P3HT fractions with different molecular weight. For powder samples, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were used to investigate the structure and crystallization behavior of the polymers. The GPC investigations show that all weight fractions possess a rather broad molecular weight distribution. DSC measurements reveal a strong decrease of the crystallization temperature and, most important, a significant decrease of the degree of crystallinity with decreasing molecular weight. To study the structure of thin layers in lateral and vertical directions, both transmission electron microscopy (TEM) and X-ray grazing incidence diffraction (GID) were utilized. These methods show that thin layers of the low molecular weight fraction consist of well-defined crystalline domains embedded in a disordered matrix. We propose that the transport properties of layers prepared from fractions of poly(3-hexylthiophene) with different molecular weight are largely determined by the crystallinity of the samples and not by the perfection of the packing of the chains in the individual crystallites.

An experimental study on the molecular organization and exciton diffusion in a bilayer of a porphyrin and poly(3-hexylthiophene)

“…In the case of first order diffraction, this peak reveals the presence of a well-developed structure directed perpendicular to the quartz substrate with an interplanar distance equal to 17.0 Å. This distance most likely corresponds to the spacing between P3HT chains along the hexyl side chains, as reported in several earlier works 23,[25][26][27] and shown schematically in Fig. 5͑b͒.…”

“…[23][24][25][26][27] The organization of polyalkylthiophene backbones has been observed to strongly affect charge transport 22,24 and may also influence the extent of exciton diffusion. In this work, the photophysical and morphological properties of a combination of the visible-light absorbing electron-accepting porphyrin derivative meso-tetrakis ͑n-methyl-4-pyridyl͒ porphyrin tetrachloride ͑H 2 TMPyP͒ and regioregular poly͑3-hexylthiophene͒ ͑P3HT͒ are presented.…”

π-Conjugated polymer-layered structures: synthesis and self-assembly

“…23 Conjugated linkers extended the π-conjugation length and the conjugated polymers can form nanofibers through their strong π-π interactions. 24,25 Among the different types of linkers, hairpin-shaped rigid linkers can promote the formation of intramolecular π-stacked structures. [26][27][28][29][30] We have recently reported the synthesis of polymers with layered aromatic rings using a xanthene scaffold as a hairpin-shaped linker; these polymers exhibit intramolecular π-stacked structures with multiple aromatic rings stacked along a single polymer chain.…”

Improving the leakage current of polyimide-based resistive memory by tuning the molecular chain stack of the polyimide film

“…By tuning the PI film density, we also altered the E int of the PI films, the distance between molecule-molecule chains, and the number of stacks of molecular chains. 29) Using this method, the electrical performance of the PI-based ReRAM was improved; for example, a high on=off ratio and a low leakage current were achieved. A conduction model of ReRAM for different PI film densities was also proposed to describe the carrier transport mechanism of the material.…”