Solid-state processing of organic semiconductors.

Solid-state processing of conjugated small molecular, oligomeric and polymeric compounds was conducted. Solid, powdered material was placed in a hot press, followed by compression molding well below the melting temperatures of the species, typically at pressures of approximately 10 30 kN cm-2. In order to investigate whether or not solid-state processing deteriorated electronic properties of the semiconductors, time-of-flight (TOF) photoconductivity experiments were conducted, which allow determination of bulk charge transport across thin film architectures. A typical small-molecular compound (6T) and two polymeric species P3HT and the liquid-crystalline PBTTT-C16, were selected. It was demonstrated that bulk carrier mobilities derived from TOF studies did not deteriorate, but in some cases actually could be significantly enhanced when compared to conventionally processed structures. Interfacial charge transport both for electrons and holes was not affected, despite processing the organic semiconductors in light and air

The impact of molecular weight on microstructure and charge transport in semicrystalline polymer semiconductors–poly(3-hexylthiophene), a model study

Electronic properties of organic semiconductors are often critically dependent upon their ability to order from the molecular level to the macro-scale, as is true for many other materials attributes of macromolecular matter such as mechanical characteristics. Therefore, understanding of the molecular assembly process and the resulting solid-state short- and long-range order is critical to further advance the field of organic electronics. Here, we will discuss the structure development as a function of molecular weight in thin films of a model conjugated polymer, poly(3-hexylthiophene) (P3HT), when processed from solution and the melt. While focus is on the microstructural manipulation and characterization, we also treat the influence of molecular arrangement and order on electronic processes such as charge transport and show, based on classical polymer science arguments, how accounting for the structural complexity of polymers can provide a basis for establishing relevant processing/structure/property-interrelationships to explain some of their electronic features. Such relationships can assist with the design of new materials and definition of processing protocols that account for the molecular length, chain rigidity and propensity to order of a given system