No abstract

Series of dyes containing a cyanovinyl entity in the spacer have been developed and characterized. Dye-sensitized solar cells (DSSCs) using the dyes as the sensitizers exhibited good efficiencies ranging from 3.48−4.92%, which reached 45−70% with respect to that of an N719-based device fabricated under similar conditions. In general, better DSSC performances are observed with molecules having a shorter distance between the internal cyanovinyl entity and the amine donor. Computational analysis indicated that the cyanovinyl entity may behave as a charge trap, especially in the long molecules studied, where the cyanovinyl group is away from the electron-donating amine by two or more aromatic groups. A positive correlation is observed between the theoretically calculated product of oscillator strengths and the charge shift at the cyanoacrylic acid group and the measured short-circuit current in DSSCs. Therefore, it is likely that the charge-trapping in the cyanovinyl entity reduces the electronic interaction between the dye and the attached TiO2 and, therefore, compromises the DSSC performance.

Series of dipolar dyes containing pyrrole-based conjugate spacers between arylamine donor and the 2-cyanoacrylic acid acceptor have been synthesized. These compounds exhibit both π-π*and charge-transfer transition in the absorption spectra. Quantum computation results indicate that the pyrrole moieties have larger dihedral angles with its neighboring units, leading to less interaction between the units and, therefore, better charge separation. It also acts as a secondary electron donor upon photoexcitation. The oxidation potentials of arylamine in these compounds are affected by the heteroaromatic conjugated spacers. Dye-sensitized solar cells (DSSCs) using these materials as the sensitizers exhibit good performance, with conversion efficiencies ranging from 4.77% to 6.18%. These values are 66-86% of the standard cell from N719 (7.19%).

New dipolar compounds incorporating a dithieno[3,2-b:2',3'-d]thiophene unit as the electron donor, an oligothiophene moiety as the conjugated spacer, and 2-cyanoacrylic acid as the electron acceptor have been synthesized. These nonarylamine type metal-free organic compounds have been successfully used as the sensitizers of dye-sensitized solar cells (DSSCs). The conversion efficiencies of the DSSCs range from 3.54 to 5.15% under AM 1.5 G irradiation. The best efficiency reached approximately 70% of the ruthenium dye N719-based standard cell fabricated and measured under similar conditions.