Variations in Semiconducting Polymer Microstructure and Hole Mobility With Spin-Coating Speed
Dean M. DeLongchamp, Brandon M. Vogel, Youngsuk Jung, Curt A. Richter, Oleg A. Kirillov, Jan Obrzut, Daniel A. Fischer, S Sambasivan, Marc Gurau, Lee J. Richter, Eric K. Lin
Organic semiconductors permit low-cost processing methods such as spin-coating, dip coating, or ink-jet printing onto flexible substrates. However, the performance of these materials in devices is difficult to control and new processing methods can deliver unexpected results. These deviations are often due to variability in film microstructure, which is sensitive to processing variables that influence the dynamic assembly process of the material as it dries from a solution to a solid thin film.For regioregular poly(3-hexyl thiophene) (P3HT), we changed spin speed to systematically vary the solvent evaporation rate, and then measured variations in the P3HT conjugated plane orientation with near edge X ray absorption fine structure (NEXAFS) spectroscopy. We find that the P3HT conjugated plane varies from an edge on to a plane on orientation as a function of the spin speed or solvent evaporation rate employed. This variation does not result in changes in surface morphology as observed by AFM, but it does correlate closely to the saturation hole mobility measured in field effect transistors.