Efficient azobenzene co-sensitizer for wide spectral absorption of dye-sensitized solar cells

Two azobenzene dyes, [Cu(azobenzene-4,4'-dicarboxylate) diethylenediamine] (ADD), [Cd(4,4'-diazenediyldibenzoato)(H₂O)] (DDB), have been designed, synthesized, and characterized as efficient co-sensitizers for dye-sensitized solar cells (DSSC). The optical, charge-transfer, electrochemical and photovoltaic properties of ADD and DDB are investigated by UV-visible spectroscopy, transient surface photovoltage measurement, cyclic voltammetry, and photocurrent-photovoltage measurement. The combination of ADD and DDB in DSSC leads to a wide spectral absorption over the whole visible range (350-700 nm). DSSC with ADD and DDB exhibits a short-circuit photocurrent density as high as 16.96 mA cm^-2, open-circuit photovoltage of 0.73 V, a fill factor of 0.57, and overall light conversion efficiency of 7.1% under standard global AM1.5 solar irradiation conditions.