Low band gap poly(1,4-arylene-2,5-thienylene)s with benzothiadiazole units: synthesis, characterization and application in polymer solar cells

We describe the synthesis of two novel poly(1,4-arylene-2,5-thienylene)s P1 and P2 containing benzo[c][2,1,3]thiadiazole monomeric units via Suzuki–Miyaura polymerization of a thiophene diboronic ester with aryl diiodides. The use of a catalyst complex consisting of Pd(OAc)2 in combination with the electron-rich biaryl phosphine S-Phos resulted in efficient polymerization reactions. The polymers synthesized, P1 and P2, were characterized by UV–vis spectroscopy and cyclic voltammetry. Theoretical calculations and electrochemical measurements on P1 suggested a favorable position of the molecular orbitals for employment in polymer solar cells in combination with PCBM. Devices containing P1:PCBM 1:2 in the active layer showed an efficiency of 1.2% by simple spin casting from chloroform