Thiophene-Functionalized Coumarin Dye for Efficient Dye-Sensitized Solar Cells:  Electron Lifetime Improved by Coadsorption of Deoxycholic Acid

• Published in: Journal of physical chemistry. C Vol. 111; no. 19; pp. 7224 - 7230
• Main Authors: Wang, Zhong-Sheng, Cui, Yan, Dan-oh, Yasufumi, Kasada, Chiaki, Shinpo, Akira, Hara, Kohjiro
• Format: Journal Article
• Language: English
• Published: American Chemical Society 17.05.2007
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp067872t

This paper reports a new coumarin dye, 2-cyano-3-(5-{2-[5-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H ,4H,10H-11-oxa-3a-aza-benzo[de]anthracen -9-yl)-thiophen-2-yl]-vinyl}-thiophen-2-yl)-acrylic acid (NKX-2700), and its application in dye-sensitized solar cells (DSSCs). Under illumination of simulated AM1.5G solar light (100 mW cm-2) with an aperture black mask, 5.0% of power conversion efficiency [short-circuit photocurrent density (J sc) = 12.0 mA cm-2, open-circuit photovoltage (V oc) = 0.59 V, and fill factor (FF) = 0.71] was obtained for NKX-2700 based DSSC, which was significantly improved to 8.2% (J sc = 15.9 mA cm-2, V oc = 0.69 V, FF = 0.75) upon addition of 120 mM deoxycholic acid (DCA) to the dye solution for TiO2 sensitization. Coadsorption of DCA decreased dye coverage by ∼50% but significantly improved the J sc by 33%. The breakup of π-stacked aggregates might improve electron injection yield and thus J sc. Electrochemical impedance data indicate that the electron lifetime was improved by coadsorption of DCA, accounting for the significant improvement of V oc. These results suggest that interfacial engineering of the organic dye-sensitized TiO2 electrodes is important for highly efficient photovoltaic performance of the solar cell.