Two Polythiophene Derivatives Containing Phenothiazine Units: Synthesis and Photovoltaic Properties

Two polythiophene derivatives containing phenothiazine units, PTZV-PT and POPTZ-PT, were synthesized by a Stille coupling reaction and characterized by UV−vis absorption spectroscopy, photoluminescence spectroscopy, and electrochemical cyclic voltammetry. The structural difference between the two polymers lies in the locations of the phenothiazine units relative to thiophene-containing polymer backbones. The phenothiazine unit acts as side chain for PTZV-PT, whereas it copolymerizes with thiophene in the polymer main chain for POPTZ-PT . Compared to POPTZ-PT, PTZV-PT exhibits a broader absorption band with an absorption edge close to 700 nm. Mobility measurements by the space-charge-limited current (SCLC) method showed that PTZV-PT exhibits a higher hole mobility (4.7 × 10 −3 cm 2 V −1 s −1 ) than POPTZ-PT (5.0 × 10 −4 cm 2 V −1 s −1 ). The polymers were used to fabricate bulk-heterojunction polymer solar cells (PSCs). The PSCs with active layers consisting of these two polymers as electron donors and the methanofullerene [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as electron acceptors delivered power-conversion efficiencies (PCEs) of 1.0% for PTZV-PT and 0.09% for POPTZ-PT . We believe that the differences in optical absorption and charge-carrier mobility are responsible for the different performances of the devices.