Thieno[3,4-b]thiophene–benzo[1,2-b:4,5-b′]dithiophene-based polymers bearing optically pure 2-ethylhexyl pendants: Synthesis and application in polymer solar cells

Abstract Optically active narrow-bandgap polymers (( R , R )- and ( S , S )-PTB5) consisting of alternating n -octyl thieno[3,4- b ]thiophene-2-carboxylate and benzo[1,2- b :4,5- b ′]dithiophene units bearing optically pure ( R )- and ( S )-2-ethylhexyl pendants, respectively, were synthesized for the first time. ( R , R )- and ( S , S )-PTB5 films showed apparent circular dichroism in their absorption regions of the polymer backbone due to the formation of a chirally ordered superstructure induced by the chirality of the branched alkyl pendants. Inverted-type bulk heterojunction polymer solar cells (PSCs) were fabricated using ( R , R )- or ( S , S )-PTB5 as electron donors and [6,6]-phenyl-C 61 -butyric acid methyl ester as an electron acceptor. The photovoltaic properties of the PSCs were compared with those of the corresponding PSC containing optically inactive PTB5 bearing racemic 2-ethylhexyl pendants.