Incorporation of Pyrene Units to Improve Hole Mobility in Conjugated Polymers for Organic Solar Cells

Abstract

Solution-processable semiconducting copolymers, poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5′-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and poly[4,8-bis(2-ethylhexyl-2-thenyl)-benzo[1,2-b:4,5-b′]dithiophene-alt-5,5′-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PBDTDTBT), and their pyrene-containing terpolymers were synthesized using Suzuki or Stille coupling. Pyrene units were introduced to improve the charge-transporting abilities of the polymers. The resulting polymers were found to be soluble in common organic solvents and formed smooth and uniform spin-coated thin films. They also exhibited good thermal stability and lost <5% of their weight upon heating to ∼350 °C. Solution-processed field-effect transistors fabricated using these polymers showed p-type organic thin-film transistor characteristics. The pyrene-containing terpolymers showed higher field-effect mobilities than their corresponding parent polymers, and their mobility increased with increasing pyrene content. Furthermore...