A compact diketopyrrolopyrrole dye as efficient sensitizer in titanium dioxide dye-sensitized solar cells

Two novel TiO2 sensitizers, based on the highly stable diketopyrrolopyrrole (DPP) skeleton, have been synthesized for application in the field of dye sensitized solar cells. The obtained dyes, DPP1 and DPP2 bear respectively a cyanoacrylic acid and a rhodanine acid anchoring groups, thus tuning the extent of the electronic communication with the semi-conducting oxide. The two chromophores were characterized by solution phase spectroscopy and electrochemistry. DFT calculations gave deeper insight into the electronic structure of both dyes, through the disclosure of their frontier orbitals. Photovoltaic performances unravelled the undisputable advantage of DPP1 over DPP2, owing to the combination of a favourable dipolar moment interaction with TiO2, and more intimate orbital blending between the chemisorbed dye and the conduction band. Chenodeoxycholic acid proved to be useful in limiting the formation of dye aggregates, improving to a great extent the performances of DPP1 based DSSCs, reaching in our conditions a 4.47% yield and 57% IPCE at 500 nm.