One of the biggest challenges in the field of semiconducting polymers is the fundamental understanding of crystallization kinetics and thin film growth. The difficulties facing such studies stem from the inherently short crystallization times of these materials and the relatively slow techniques available for characterizing nanoscale microstructures. To overcome these limitations, we chose to investigate the polymer poly(3-ethylhexylthiophene) (P3EHT). Due to its low melting point, P3EHT exhibits slow crystallization kinetics when quenched at room temperature from the melt, which is a rare property among semiconducting polymers. We perform quantitative analyses of x-ray diffraction patterns and optical absorption spectra P3EHT thin films and are able to monitor the evolution of aggregates and crystallites as well as the recrystallization kinetics as a function of time. Here we find that the growths of individual aggregates and crystallites along the three packing directions are indeed anisotropic and exhibit different growth rates. Furthermore, we show that crystallization kinetics depend on a number of parameters including film thickness, molecular weights and quenching temperatures, which is all attributed to chain confinement effects. Finally we also correlate the evolution of thin film microstructure to electronic properties and charge transport. From these measurements, we directly observe the onset of charge percolation in thin film and demonstrate that polymer tie chains are responsible for efficient charge transport.
