A Semiconducting Liquid Crystalline Block Copolymer Containing Regioregular Poly-(3-hexylthiophene) and Nematic Poly(n-hexyl Isocyanate) and its Application in Bulk Heterojunction Solar Cells

A liquid crystalline diblock copolymer containing regioregular poly(3-hexylthiophene) (P3HT) and poly-(n-hexyl isocyanate) (PHIC) was synthesized by the combination of Grignard metathesis polymerization (GRIM) and titanium mediated coordination polymerization methods. The poly(3-hexylthiophene)-b-poly(n-hexyl isocyanate) (P3HT-b-PHIC) diblock copolymer used in this study contained ~10 mol% of P3HT and ~90 mol% of PHIC. The diblock copolymer displayed solvatochromism in THF-water and THF-methanol mixtures. The field-effect mobilities of the synthesized block copolymer were measured in bottom gate-bottom contact organic field-effect transistors (OFETs). The surface morphology of the polymer thin film was investigated in the channel region of the OFET devices by tapping mode atomic force microscopy (TMAFM). The diblock copolymer displayed nanostructured morphology in thin film and had good mobility despite the low content of the semiconducting P3HT block. The diblock copolymer was also used as an additive to improve the performance of P3HT/PCBM bulk heterojunction (BHJ) solar cells. Liquid crystalline characteristics of the diblock copolymer were examined by cross-polarizing microscopy and X-ray diffraction.