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.