Today renewable energy is a hot topic, both in academic and in industrial research, due to the request of sustainable energy sources; of course, in the more specific field of photovoltaics, dye-sensitized solar cells may represent an alternative low-cost kind of device. In particular, in the last years, push-pull meso disubstituted porphyrins have shown the best photon-to-electron conversion efficiencies as sensitizers in these kind of solar cells,1 however, these dyes can be obtained only by a multistep synthesis with very low total yields. In this work, a facile and fast approach, based on microwave enhanced Sonogashira coupling, was employed to obtain, with good yields, both mono and, for the first time, disubstituted push-pull ZnII-porphyrinates bearing a variety of ethynylphenyl moiety in b-pyrrolic position. Furthermore a comparative experimental, electrochemical and theoretical investigation was carried out between such b mono or disubstituted ZnII-porphyrinates and meso disubstituted push-pull ZnII-porphyrinates. We produced evidence that, although the HOMO-LUMO energy gap of the meso disubstituted push-pull dyes is lower, so that the charge transfer along the push-pull system is easier for these latter, the b mono or disubstituted push-pull porphyrinic dyes show comparable or better efficiencies when acting as sensitizers in DSSCs. This behaviour is probably due to a more facile charge injection into TiO2 surface as suggested by the DFT electron distribution and by the positive effect of the b substitution on the IPCE spectra, which show a relevant intensity over a broad range of wavelengths (350-650 nm). Finally the positive effect due to the presence of a cyanoacrylic group in the ethynyl-phenyl substituent has been analysed with a photophysical and theoretical approach supporting the evidence of a contribution of charge transfer transitions to both the B and Q bands, thus producing, by conjugation, excited electrons close to the carboxylic anchoring group.
Porphyrin sensitizer solar cell: a comparison with meso disubstituted push-pull and ?-pyrrolic ZnII-porphyrinates
A Orbelli Biroli;F De Angelis;
2013
Abstract
Today renewable energy is a hot topic, both in academic and in industrial research, due to the request of sustainable energy sources; of course, in the more specific field of photovoltaics, dye-sensitized solar cells may represent an alternative low-cost kind of device. In particular, in the last years, push-pull meso disubstituted porphyrins have shown the best photon-to-electron conversion efficiencies as sensitizers in these kind of solar cells,1 however, these dyes can be obtained only by a multistep synthesis with very low total yields. In this work, a facile and fast approach, based on microwave enhanced Sonogashira coupling, was employed to obtain, with good yields, both mono and, for the first time, disubstituted push-pull ZnII-porphyrinates bearing a variety of ethynylphenyl moiety in b-pyrrolic position. Furthermore a comparative experimental, electrochemical and theoretical investigation was carried out between such b mono or disubstituted ZnII-porphyrinates and meso disubstituted push-pull ZnII-porphyrinates. We produced evidence that, although the HOMO-LUMO energy gap of the meso disubstituted push-pull dyes is lower, so that the charge transfer along the push-pull system is easier for these latter, the b mono or disubstituted push-pull porphyrinic dyes show comparable or better efficiencies when acting as sensitizers in DSSCs. This behaviour is probably due to a more facile charge injection into TiO2 surface as suggested by the DFT electron distribution and by the positive effect of the b substitution on the IPCE spectra, which show a relevant intensity over a broad range of wavelengths (350-650 nm). Finally the positive effect due to the presence of a cyanoacrylic group in the ethynyl-phenyl substituent has been analysed with a photophysical and theoretical approach supporting the evidence of a contribution of charge transfer transitions to both the B and Q bands, thus producing, by conjugation, excited electrons close to the carboxylic anchoring group.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
