Isoindigo-3,4-Difluorothiophene Polymer Acceptors Yield 'All-Polymer' Bulk-Heterojunction Solar Cells with over 7 % Efficiency.

Poly(isoindigo- alt-3,4-difluorothiophene) (PIID[2F]T) analogues used as 'polymer acceptors' in bulk-heterojunction (BHJ) solar cells achieve >7 % efficiency when used in conjunction with the polymer donor PBFTAZ (model system; copolymer of benzo[1,2- b:4,5- b′]dithiophene and 5,6-difluorobenzotriazole). Considering that most efficient polymer-acceptor alternatives to fullerenes (e.g. PC61BM or its C71 derivative) are based on perylenediimide or naphthalenediimide motifs thus far, branched alkyl-substituted PIID[2F]T polymers are particularly promising non-fullerene candidates for 'all-polymer' BHJ solar cells. [ABSTRACT FROM AUTHOR]