Dye-sensitized solar cells using a chlorophyll a derivative as the sensitizer and carotenoids having different conjugation lengths as redox spacers

Titania-based Grätzel-type solar cells were fabricated by the use of a chlorophyll a derivative (methyl 3-carboxy-3-devinyl-pyropheophorobide a) as the dye sensitizer. A 10% each of carotenoids, including neurosporene, spheroidene, lycopene, anhydrorhodovibrin and spirilloxanthin with numbers of conjugated double bonds, n = 9–13, was added as a conjugated spacer in order to neutralize the dye radical cation and to block the reverse electron transfer. The short-circuit current density (Jsc) and the solar energy-to-electricity conversion efficiency (η) systematically increased, with increasing n, from the values of 10.1 mA cm−2 and 3.1% (with no carotenoid) up to 11.5 mA cm−2 and 4.0% (with spirilloxanthin, n = 13), i.e., an enhancement of ≈30%.