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Self Encapsulated Poly(3-hexylthiophene)-poly(fluorinated alkyl methacrylate) Rod-Coil Block Copolymers with High Field Effect Mobilities on Bare SiO2

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Abstract

Conjugated rod-coil block copolymers provide an interesting route towards enhancing the properties of the conjugated block due to self-assembly and the interplay of rod-rod and rod-coil interactions. Here, we demonstrate the ability of an attached semi-fluorinated block to significantly improve upon the charge carrier properties of regioregular poly(3-hexyl thiophene) (rr-P3HT) materials on bare SiO2. The thin film hole mobilities on bare SiO2 dielectric surfaces of poly (3-hexyl thiophene)-block-polyfluoromethacrylates (P3HT-b-PFMAs) can approach up to 0.12 cm2 V−1 s−1 with only 33 wt% of the P3HT block incorporated in the copolymer, as compared to rr-P3HT alone which typically has mobilities averaging 0.03 cm2 V−1 s−1. To our knowledge, this is the highest mobility reported in literature for block copolymers containing a P3HT. More importantly, these high hole mobilities are achieved without multistep OTS treatments, argon protection, or post-annealing conditions. Grazing incidence wide-angle x-ray scattering (GIWAX) data revealed that in the P3HT-b-PFMA copolymers, the P3HT rod block self-assembles into highly ordered lamellar structures, similar to that of the rr-P3HT homopolymer. Grazing incidence small-angle x-ray scattering (GISAXS) data revealed that lamellar structures are only observed in perpendicular direction with short PFMA blocks, while lamellae in both perpendicular and parallel directions are observed in polymers with longer PFMA blocks. AFM, GIWAXS, and contact angle measurements also indicate that PFMA block assembles at the polymer thin film surface and forms an encapsulation layer. The high charge carrier mobilities and the hydrophobic surface of the block copolymer films clearly demonstrates the influence of the coil block segment on device performance by balancing the crystallization and microphase separation in the bulk morphological structure.

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