We have examined the effects of crystallization kinetics of poly(3-hexylthiophene) and poly[2,5-bis(3-hexadecylthiophen-2-yl)thieno(3,2-b) thiophene] on microstructure and charge transport. Rapid crystallization increases the density of tie molecules in polythiophenes. As a consequence, ordered regions are better connected resulting in higher charge carrier mobilities. Our results suggest that controlling the crystallization kinetics might be an important factor for maximizing the charge mobility in semicrystalline polythiophene thin films. The crystallization kinetics can affect the microstructure and consequently charge transport of polythiophenes by changing the density of tie molecules. Rapid crystallization of P3HT and PBTTT results in higher density of tie molecules and higher charge carrier mobility. This suggests that controlling the crystallization kinetics might be an important factor for maximizing the charge mobility in semicrystalline polythiophene thin films. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.