Influence of the Anchoring Modes on the Electronic and Photovoltaic Properties of D-π-A Dyes

Five new donor-pi-bridge acceptor (D-pi-A) organic sensitizers with cyano and/or triple bond substituted benzoic acid as acceptor/anchoring groups were synthesized and tested for their performance in dye-sensitized solar cells (DSCs). The systematic incorporation of a cyano group on the benzoic acid anchoring part and an additional acetylene bond at the para-position to -COOH lead to a variation of the photoelectrochemical properties, electronic transitions, and device performances. Characterization of the molecular structure, the electronic/optical properties of the dyes, as well as their photovoltaic performance in DSCs was accomplished by means of electrochemistry, quantum chemical methods, and various spectroscopic techniques such as photoinduced absorption, steady-state spectroscopy, and time-resolved transient absorption studies on femto- and nanosecond time scales. Thereby, significant dependence of DSCs performances on the substituents and anchoring groups was observed. In general, cyano substituents lead to improved DSCs performances. On the other hand, the insertion of an acetylene linker in combination with a cyano group does not enhance the device efficiencies. Devices composed of a para-cyano benzoic acid as anchor revealed maximum IPCE values of 80% with a PCE of 4.50% at AM 1.5 G illumination (100 mW cm(-2)) due to retarded charge recombination dynamics.