A Study Of Dyes With Lateral Anchoring Group For Dye-sensitized Solar Cells

As an effective way of using solar energy, the dye-sensitized solar cells (DSC) have attracted considerable attention around the world. Photosensitizer, which absorbs the sunlight and injects electrons into the conduction band of TiO2, is one of the most important parts of DSC. The metal-free organic dyes, which are known as the tailor-made sensitizers have been developed rapidly in recent years due to their advantages of low-cost and promising efficiency.In this paper, two novel metal-free organic dyes were designed and synthesized as sensitizers for DSC. In this series of dyes, N, N-dihexyl substituted aniline unit was used as the electron donor, m-nitrobenzonitrile unit was adopted as the electron acceptor, lateral chain propanoic acid was acted as the anchoring group, thiophene and 3,4-ethylenedioxythiophene was acted asπ-conjugation. Compared with traditional donor-conjugation-acceper (D-π-A) dyes (using cyanoacrylic acid as acceptor and the anchoring group), the anchoring group in these dyes were separated from the acceptor units, which allows us to tune the HOMO-LUMO level (absorption spectra) in an easier way by modifying the structure of the acceptor units.Meanwhile, the structures of the dyes were characterized by High Resolution Mass Spectra (HRMS) and Proton Nuclear Magnetic Resonance ('H NMR) technology. The photophysical and electrochemical properties of the dyes were studied.It is found that different dye-baths for the sensitization of TiO2 have a crucial effect on the performance of the DSC due to the different absorption spectra. Eventually acetonitrile was adopted as dye-bath solvent.At the beginning of the J-V test, the DSC almost had no efficiency probably due to that no injection of the electrons from the dye to the conduction band of TiO2. During the test of J-V, the color of the dyes on the TiO2 changed from red to light yellow, while the efficiency improved. We can speculate by FT-IR and experimental phenomenons that may be the-NO2 of the dyes bonded with the TiO2 at the existence of electrolyte during the J-V test, which let the electrons inject from the dyes to the bond of TiO2 effectively. Finally, the dye with thiophene asπ-conjugation achieved a higherηvalue of 0.93%(short-circuit photocurrent density Jsc= 1.92 mA.cm-2, open-circuit photovoltage Voc=0.62 V and fill factor ff=0.78). Under 100 mW cm-2 (AM 1.5 G).