Yuyin Xi

Macroscopically aligned nanowire arrays of π-conjugated polymers via shear-enhanced crystallization

The nanoscale structure and macroscopic morphology of π-conjugated polymers are very important for their electronic application. While ordered single crystals of small molecules have been obtained via solution deposition, macroscopically aligned films of π-conjugated polymers deposited directly from solution have always required surface modification or complex pre-deposition processing of the solution. Here, ordered nanowires were obtained via shear-enhanced crystallization of π-conjugated polymers at the air–liquid–solid interface using simple deposition of the polymer solution onto an inclined substrate. The formation of macroscopically aligned nanowire arrays was found to be due to the synergy between intrinsic (π-conjugated backbone) and external (crystallization conditions) effects. The oriented nanowires showed remarkable improvement in the charge carrier mobility compared to spin-coated films as characterized in organic field-effect transistors (OFETs). Considering the simplicity and large-scale applicability, shear-enhanced crystallization of π-conjugated polymers provides a promising strategy to achieve high-performance polymer semiconductor films for electronics applications.

Acoustic wave directed assembly of conjugated polymers

Conjugated polymers (CP) have attracted a great deal of attention because they are flexible, light weight, economical, and highly scalable. They are widely used in organic electronics, such as organic field effect transistors, photovoltaics, thermoelectrics, spintronics and electronic skins. However, the electrical performance of CP is still limited due to the inefficient charge hopping between polymer chains.

Structure and dynamics of conjugated polymers from scattering and simulations

Conjugated polymer films, nanofibers, and networks can be ideal materials for the design of efficient photovoltaic devices, batteries, thermoelectric cells, light emitting diodes and many emerging technologies.[1] It is also recognized that the structure and dynamics of organic semiconductor materials correlates strongly with large changes in optical, electronic and mechanical properties so that their control and manipulation is essential to advancing the field. This presentation outlines the use of neutron scattering techniques in the development of structure-property relationships for conjugated polymer nano materials.[2] It also highlights recent results on the use of neutron and x-ray scattering techniques for the development of improved molecular simulation force fields and structural parameters specifically produced for conjugated polymers. Quasi-elastic neutron scattering (QENS) experiments are used along with computationally efficient MD simulations to understand the nature of important nanoscale motions. X-ray and polarized neutron diffraction are also used to correlate experimental and model-generated polymer structures. QENS validation of MD force fields presents a unique opportunity to increase the accuracy of highly uncertain parameters used in simulation of conjugated polymers such as partial charges and backbone torsion. These parameters are currently estimated from quantum mechanical calculations such as density functional theory but, unlike many force fields for small molecules, are not parameterized with available experimental data. High variability is observed in these parameters for the small number of force fields that have been proposed in the literature. A vision for the accelerated development of accurate force fields for these classes of materials is also proposed.