End-on orientation of poly(3-alkylthiophene)s by microphase separation of amphiphilic diblock copolymer*

To fabricate end-on orientation of poly(3-alkylthiophene) (P3AT) where the polymer main chains are vertically oriented on the substrate, we synthesized poly(3-dodecylthiophene)-block-poly(3-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methylthiophene) copolymer (P3DDT-b-P3TEGT) using the GRIM method. P3DDT-b-P3TEGT showed lamellar microdomains, confirmed by SAXS. The thin film morphology measured by AFM and GIWAXS showed parallel oriented lamellar microdomains on a substrate, because of a large difference of surface tension between hydrophobic P3DDT and hydrophilic P3TEGT blocks. In this geometry, both P3DDT and P3TEGT backbone chains were oriented perpendicularly to the lamellar layer; thus the end-on orientation of P3DDT chains was obtained. P3DDT-b-P3TEGT film showed much improved hole mobility compared with neat P3DDT film in spite of presence of P3TEGT block with low hole mobility. Once one can design lamellar forming block copolymers having higher mobility than P3DDT and P3TEGT, much higher hole mobility would be expected, which is very useful for designing high performance vertically operating devices.