Novel Low Band Gap Phenylenevinylene Copolymer with BF2−Azopyrrole Complex Units: Synthesis and Use for Efficient Bulk Heterojunction Solar Cells

Abstract

An alternating phenylenevinylene copolymer (P) was synthesized by Heck coupling of 2,5-bis[2-(4-bromophenyl)diazeny]-1H-pyrrole with 1,4-divinyl-2,5-bis(hexyloxy)-benzene. The subsequent reaction of P with boron trifluoride diethyl etherate afforded the corresponding BF2−azopyrrole complex (PB) which was used for bulk heterojunction solar cells. A thin film of PB showed a broad absorption band with a long-wave absorption maximum at 511 nm and an optical band gap of 1.63 eV. We have used a solvent mixture consisting of THF with various contents of acetone, in order to prepare the PB:PCBM blend films for polymer bulk heterojunction (BHJ) photovoltaic (PV) devices. Since the vapor pressure of the solvent mixture is lower compared to neat THF, the blend films dried slowly and nanoparticles of PB are formed, as indicated by the XRD pattern. The correlation of PB nanoparticles with PV properties of the PB:PCBM BHJ devices was investigated. It was found that the optical absorption and hole transport in the resul...