Enhanced Vertical Hole Mobility through End-on Chain Orientation of Poly(3-hexylthiophene)-based Diblock Copolymers by Microphase Separation

We synthesized the poly(3-hexylthiophene)-block-poly(3-(2-methoxyethoxy)methylthiophene) copolymer (P3HT-b-P3MEGT) with a regioregularity (RR) of the P3HT block having 82% to obtain an end-on orientation throughout the entire film thickness. Although P3HT-containing block copolymers with high RR = 86% of the P3HT block showed fibril morphology because of strong rod-rod interaction of P3HT, P3HT-b-P3MEGT with RR = 82% of P3HT exhibited a well-defined lamellar morphology induced by microphase separation between P3HT and P3MEGT blocks. P3HT-b-P3MEGT thin films showed parallel-oriented lamellar nanostructures on a silicon substrate because of a large difference in surface tension between hydrophobic P3HT and hydrophilic P3MEGT blocks. Parallel-oriented lamellar nanostructures induced the end-on orientation of P3HT and P3MEGT chains across the entire film. End-on-oriented P3HT-b-P3MEGT thin films showed much enhanced vertical hole mobility, 30 times higher than that of edge-on-oriented P3HT homopolymer thin films with a high RR of 95%.