Effect of Anchoring Group on Electron Injection and Recombination Dynamics in Organic Dye-Sensitized Solar Cells

In the field of dye-sensitized solar cells the no. of different sensitizing dyes is increasing rapidly. To produce low-cost dyes, much work is being directed toward synthesizing all-org., Ru-free dyes with high extinction coeffs. and broad absorption bands with large solar spectrum overlap. One of the best dyes, the polyene-diphenylaniline dye D5L2A1, has a rather blue absorption with an IPCE onset at ∼650 nm, but it still has an energy conversion efficiency of almost 6%. To increase the overlap with the solar spectrum, the cyanoacrylic acid anchoring group was changed to rhodanine-3-acetic acid in the complex D5L2A3. This gave an IPCE onset at ∼750 nm, but unfortunately, it also decreased the overall efficiency to a modest 1.7%. By femtosecond transient absorption, the electron injection into TiO2 for the 2 dyes are ultrafast and indistinguishable with the time resoln. (