Betalain pigments for dye-sensitized solar cells

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2008-03, Vol.195 (1), p.72-80
• Main Authors: Zhang, Dongshe, Lanier, Suzanne M., Downing, Jonathan A., Avent, Jason L., Lum, June, McHale, Jeanne L.
• Format: Article
• Language: English
• Subjects: Betalains; Dye-sensitized solar cell; Plant pigments
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2007.07.038

A dye-sensitized solar cell based on natural betalain pigments from red beet roots is described. Reddish-purple betanin is an easily oxidized, water-soluble pigment with strong visible light absorption, having a maximum molar absorptivity of about 65,000 M −1 cm −1at 535 nm. A photoanode was fabricated from nanocrystalline TiO 2 on transparent conductive glass, treated with ethanolic HCl solution, then sensitized with raw beet extract or a betanin solution from which yellow betaxanthin pigments were removed by column chromatography. The betanin-sensitized film when employed in a dye-sensitized solar cell gave a maximum photocurrent of 2.42 mA/cm 2 and open-circuit photovoltage of 0.44 V in the presence of methoxypropionitrile containing I −/I 3 − redox mediator. Photocurrents and photovoltages are also reported for the DSSC sensitized with yellow betaxanthin and a brown betalain-derived oxidation product. Wavelength-dependent incident photon-to-electron conversion efficiencies (IPCEs) show maximum values of 14% and 8% for betaxanthin- and betanin-based solar cells, respectively.