Effects of donor position on dibenzofulvene-based organic dyes for photovoltaics

A series of push-pull organic dyes based on the cyanoacrylic acid as the acceptor/anchoring group, a dibenzofulvene (DBF) connected with thienyl rings as the ?-bridge, and donor units linked to different positions of the DBF molecule were synthetized and studied. The effects of the donor position on optical and photovoltaic properties were investigated through photophysics, electrochemical and photovoltaic measurements. The results uphold photovoltaic performances largely depend on the electronic structure of the dyes with a synergistic interaction between donor and acceptor groups. In detail, a fine tuning of the photophysical properties can be reached simply selecting the position of the donor unit on the DBF molecule. In particular, the dyes bearing the donor unit on the 3,6-positions of the DBF show better performances in term of light absorption and cell efficiency with respect to the dyes with the donor unit on the 2,7-positions.