A Polymer Blend Approach for Creation of Effective Conjugated Polymer Charge Transport Pathways.

Understanding the role of the distribution of polymer chain lengths on process-structure-property relationships in semiconducting organic electronics has remained elusive due to challenges in synthesizing targeted molecular weights (Mw) and polydispersity indices (PDI). Here, a facile blending approach of various poly(3-hexylthiophene) (P3HT) molecular weights is used to investigate the impact of the distribution of polymer chain lengths on self-assembly into aggregates and associated charge transport properties. Low and high Mw samples were blended to form a highly polydisperse sample which was compared to a similar, medium Mw control. Self-assembly was induced by preprocessing the polymer solution with ultraviolent (UV) irradiation and subsequent solution aging before deposition via blade-coating. Superior charge carrier (hole) mobilities were observed for the blend and control samples. Further, their solution lifetimes exceeded 14 days. UV-vis spectral analysis suggests that low Mw P3HT lacks the mesoscale crystallinity required for percolative charge transport. In contrast, when the Mw is too high, the polymer rapidly aggregates, leading to paracrystalline disorder and structural inhomogeneity that interrupts charge transfer pathways. The role of grain boundaries, fibrillar order, and macroscale alignment is characterized via grazing incidence wide angle x-ray scattering (GIWAXS), atomic force microscopy, (AFM) and optical microscopy techniques. The results presented here provide additional guidance on the interplay between polymer solubility, self-assembly, network interconnectivity and charge transport to enable robust polymer ink formulations with reliable and reproducible performance attributes.