Multi-Branched Multi-Anchoring Metal-Free Dyes for Dye-Sensitized Solar Cells

Multi-branched multi-anchoring metal-free dyes as photo-sensitizers for dye-sensitized solar cells (DSSCs) are reviewed. The article outlines design strategies, main synthetic routes and optical and photovoltaic properties of two families of multi-branched sensitizers: (a) D-(pi-A)(n) (D = donor, pi = pi-spacer, A = acceptor/anchoring functionality) structures containing arylamine, carbazole, phenothiazine or phenoxazine derivatives as D groups, and (b) multi-donor multi-anchoring architectures from interconnected mono-branched D-pi-A arms, together with X- and Y-shaped dyes. Although this class has been reported only in the last five years, a variety of molecular architectures, donors, and pi-spacers have been used and combined in multi-branched molecules. The multi-branched geometry induces distinctive features including enhanced qualitative and quantitative optical properties, increased currents and quantum efficiencies, and control of molecular aggregation.