Felix P. V. Koch

A general relationship between disorder, aggregation and charge transport in conjugated polymers

Conjugated polymer chains have many degrees of conformational freedom and interact weakly with each other, resulting in complex microstructures in the solid state. Understanding charge transport in such systems, which have amorphous and ordered phases exhibiting varying degrees of order, has proved difficult owing to the contribution of electronic processes at various length scales. The growing technological appeal of these semiconductors makes such fundamental knowledge extremely important for materials and process design. We propose a unified model of how charge carriers travel in conjugated polymer films. We show that in high-molecular-weight semiconducting polymers the limiting charge transport step is trapping caused by lattice disorder, and that short-range intermolecular aggregation is sufficient for efficient long-range charge transport. This generalization explains the seemingly contradicting high performance of recently reported, poorly ordered polymers and suggests molecular design strategies to further improve the performance of future generations of organic electronic materials.

Controllable Processes for Generating Large Single Crystals of Poly(3‐hexylthiophene)

Sowing the seeds: A simple strategy based on self-seeding allows large single crystals of long regioregular poly(3-hexylthiophene) chains to be grown from solution. When appropriately crystallized, materials differing in their degrees of regioregularity and molecular weights formed monoclinic form II crystals with interdigitated hexyl side groups (see picture).

Thermal and structural characteristics of oligo(3-hexylthiophene)s (3HT)n, n = 4-36.

This study is concerned with the thermal and structural characteristics of a series of precisely defined, monodisperse, regioregular oligo(3-hexylthiophene)s (3HT)n of n = 4-36. We find that these model compounds can feature two distinctly different solid-state structures, i.e., the more classical polymorph Form I in which the hexyl side-chains are not interdigitated and Form II in which they are. The thermodynamic equilibrium melting temperatures of these phases differ as much as ~180 °C, with 116 °C for Form II and 298 °C for Form I. Furthermore, polymorph II featured an enthalpy of melting of ~3 times that of Form I and a rate of crystallization that is ~1 order of magnitude lower than that of Form I. A crossover of the thermodynamically preferred Form II into the kinetically favored Form I is observed at a number of repeat units of 12. In the regime 10 ≤ n ≤ 21 the oligo(3-hexylthiophene)s could readily be reversibly converted from one polymorph to another by appropriate processing treatments. The relevance of these findings for the polymeric form (P3HT) is discussed.

“Fibonacci’s Route” to Regioregular Oligo(3-hexylthiophene)s

We describe a new synthetic approach to regioregular monodisperse oligo(3-alkylthiophene)s allowing for simple separation of regioregular material in gram quantities. The number of repeat units follows the Fibonacci numbers up to a length of 21. In a small adaption of this approach, introduction of a protecting group was used to synthesize an oligo(3-hexylthiophene) with 36 repeating units, the longest regioregular 3-hexylthiophene oligomer synthesized to date.

Solid‐State Processing of Organic Semiconductors

By Mohammed A. Baklar , elix F Koch , Avinesh Kumar , Ester Buchaca Domingo , Mariano Campoy-Quiles , Kirill eldman , F Liyang u , Y Paul Wobkenberg , James Ball , Rory M. Wilson , Iain McCulloch , Theo Kreouzis , Martin Heeney , Thomas Anthopoulos , Paul Smith ,