Design and synthesis of side-chain functionalized regioregular poly(3-hexylthiophene)-based copolymers and application in polymer:fullerene bulk heterojunction solar cells

Abstract

set of novel regioregular poly(3-hexylthiophene)-based random copolymers containing varying ratios of ester functionalized alkyl side chains were synthesized using the Rieke method. The percentage of functionalized side chain varied between 10 and 50 mol% for each copolymer. Using post-polymerization reactions, the ester functions in the alkyl side chain were hydrolyzed to yield an alcohol or acid group. These groups are available for further functionalization reactions, so a wide variety of secondary functionalities may be covalently attached to the conjugated polymer. The copolymers were applied in polymer: fullerene bulk heterojunction solar cells (BHJSCs) with [6,6]-phenyl -C61-butyric acid methyl ester (PCBM) as electron acceptor. The influence of side-chain functionalities on absorption, device performance and layer morphology depends on the ratio and nature of the functionalized side chains. For a 9/1 copolymer, containing 10% of functionalized side chains, behaviour and efficiency in BHJSCs comparable to P3HT:PCBM solar cells were observed.