(34c) Connecting Crystalline Domains: Blending Conjugated Polymers of Differing Molecular Weights for Enhanced Charge Transport

Solution processability has brought significant attention to organic electronics as low cost alternatives to traditional inorganic electronics. Ordered self-assembly of semiconducting polymers in solution enhances charge transport in processed organic thin film transistors due to percolated crystalline domains on the mesoscale. However, methods to induce so-called “tie chains” between crystalline nanofibers are lacking. Here, we propose blending high (95 kDa) and low (37 kDa) molecular weight mixtures of poly(3-hexythiophene) (P3HT) with wide polydispersity to elucidate the relationship between tie chain formation and two-dimensional charge transport. Ultraviolet-irradiation and solution aging was utilized to induce aggregation of mixtures of high and low molecular weight P3HT. Solutions were subsequently blade-coated on bottom gate, bottom contact transistors to record field effect transistor charge mobility. Using atomic force microscopy (AFM) image analysis, it was found that increasing the percentage of high molecular P3HT resulted in increased fiber density and improved orientation of fibers in the direction of blade coating. However, optimal charge mobility occurred at a 50% mixture of high and low molecular weight P3HT, indicating a tradeoff between tie chain formation and aggregate phase separation. The development of shoulder peaks in solution UV-vis spectra and increased film UV-vis dichroic ratio values provide further support of this tradeoff. These further suggest the important of tie chains for enhanced charge transport in polymeric semiconductors but also provide new guidance for conjugated polymer synthesis.