Effect of Extended π-Conjugation of the Donor Structure of Organic D-A-π-A Dyes on the Photovoltaic Performance of Dye-Sensitized Solar Cells

Two new D-A-pi-spacer-A organic dyes, KM-10 and KM-11, containing a benzothiadiazole unit in a pi-spacer and a cyanoacrylic acid as an acceptor have been synthesized and tested as sensitizers in dye-sensitized solar cells. Structural variations of the donor moiety, i.e., pi-extension of the diphenylamine electron-donating groups, gave rise to different photovoltaic efficiencies-7.1% for KM-10 and 8% for KM-11 despite having comparable absorption properties. A detailed investigation, including transient photocurrent and photovoltage decay measurement, transient absorption spectroscopy, and quantum chemical methods, provided important conclusions about the nature of the substitution on the photovoltaic properties of dyes.