Thiophene-functionalized coumarin dye for efficient dye-sensitized solar cells: Electron lifetime improved by coadsorption of deoxycholic acid

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 similar to 50% but significantly improved the J(sc) by 33%. The breakup of pi-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.