Ladder-type pentaphenylene dyes for dye-sensitized solar cells

A series of donor-pi-acceptor dyes based on rigid ladder-type pentaphenylene spacers 1-3 have been synthesized from dibromopentaphenylene 4 in three steps. The three dyes contain the same acceptors (2-cyanoacrylic acid) as anchor groups but differ in donor units (diphenylamino 1, phenothiazinyl 2, and bis(N,N-4-dimethylaminophenyl)amino 3). Their maximum absorption peaks range from 442 to 457 nm with high extinction coefficients, while dye 3 shows a broader absorption band in the visible region along with a weak NIR absorption band due to the formation of amino radical cation. The DSSCs based on these dyes demonstrate the highest IPCE value of 73% and power conversion efficiency of 2.3% (liquid cell) and 0.8% (solid cell), respectively. Although the power conversion efficiencies are not so high, this work explores new donor - spacer - acceptor models and the effects of molecular design on photophysical and photoelectrochemical properties.