Engineering diketopyrrolopyrrole sensitizers for highly efficient dye-sensitized solar cells: enhanced light harvesting and intramolecular charge transfer

Two asymmetric DPP dyes with a D-pi-A structure are reported, where DPP is used as a bridge to connect the triphenylamine donor and cyanoacetic acid acceptor. The compact dyes exhibit high light absorption ability covering the whole visible spectral region. The most efficient cell exhibited a short-circuit current density of 17.72 mA cm(-2), an open-circuit voltage of 725 mV, and a fill factor of 74%, yielding a power conversion efficiency of 9.51% under standard test conditions (irradiation of 1000 W m(-2), air mass 1.5 G), which is the highest value reported for DPP-based DSCs employing an I (-)/I-3-redox couple. Furthermore, the DPP dyes show remarkable stability under long-term irradiation over 1000 h. Considering the facile synthesis and excellent stability, the DPP sensitizer would be a promising option for highly efficient DSCs. The results show that judicious molecular engineering is crucial for constructing highly efficient charge transfer sensitizers in DSCs.