Metal‐Free and Fluorescent Diketopyrrolopyrrole Fluorophores for Dye‐Sensitized Solar Cells

Novel metal‐free and fluorescent dipyrrolopyrrole (DPP) dyes consisting of a central bis(lactam)‐bearing pendent benzyl or branched hydrocarbon groups as solubilizing fragments and two orthogonal side arms (dimethylaminopropyne and benzoate anion) have been designed and synthesized. The UV/Vis absorption spectra recorded in THF are dominated by intense low‐energy π–π* absorptions centered at 488 nm or 602 nm, respectively, for the phenyl‐ or thiophene‐based DPP dyes. The fluorescence spectra also display broad bands at 555 nm ( Φ F =0.57 and τ F =4.6 ns) for the phenyl‐ and at 624 nm ( Φ F =0.31 and τ F =3.5 ns) for the thiophene‐based molecular structures. Under standard global AM 1.5G irradiation a maximum photon‐to‐electron conversion efficiency of 2.54 % was achieved with dye‐sensitized solar cells based on nanocrystalline TiO 2 ( J sc =7.5 mA cm −2 , V oc =0.49 V, and FF =0.70) for the phenyl‐based DPP dye and 1.89 % ( J sc =7.1 mA cm −2 , V oc =0.41 V, and FF =0.65) for the thiophene‐based DPP dye.