We report on the synthesis and the photophysical/electrochemical characterization of one of the smallest and most compact dye molecules ever used as sensitizer in a dye-sensitized solar cell with obtained conversion efficiencies well above 3%. This novel molecule, a hemi-squaraine based organic dye (CT1) has been synthesized, fully characterized and used to sensitize titanium dioxide-based dye sensitized solar cells (DSSCs). The squarate moiety acts as anchoring linker on the titania surface. The dye has a molecular weight of 319 uma, a maximum absorption wavelength at 348 nm, a maximum emission wavelength at 465 nm and a molar extinction coefficient of 13234 Lmol-1cm-1. CT1 sensitized DSSCs were fabricated using a cell based on a customized microfluidic architecture, constituted by a PDMS membrane reversibly sealed between the two transparent electrodes with a PMMA clamping . The loading, aggregation and degradation of the dye were analyzed by means of UV-Vis absorption and fluorescence emission spectroscopy. The dependence of the microfluidic cell efficiency on dye incubation time, dye aggregation and TiO2 thickness was studied by I-V electrical characterization, electrochemical impedance spectroscopy (EIS) and incident photon-to-electron conversion efficiency (IPCE) measurements. A short-circuit current density of 7.89 mAcm−2, an open-circuit voltage of 0.64 V and a fill factor of 0.70 were obtained under standard AM 1.5G irradiation (1000 Wm−2), with an overall solar-to-electricity conversion efficiency of 3.54%. These results suggest that the small organic dye CT1 is highly promising as sensitizer in DSSC fabrication and the use of squarate as linking group could be efficiently further exploited for organic dye-based DSSCs.
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