Diphenylphosphinic acid (DPPA) was adopted as a novel coadsorbent in dye-sensitized solar cells (DSCs) based on nanocrystalline TiO2 sensitized with N719 dye [(Bu4N)(2)[Ru(dcbpyH)(2)(NCS)(2)]], leading to a significant enhancement of the cell's performance. Different ratios of dye-to-coadsorbent caused varying results, including a 12.5% increase in overall conversion efficiency coupled with a 10.6% increase in short-circuit current with a ratio of 2:1. Electrochemical impedance spectroscopy (EIS) results indicated that the augment ascribes to inhibited interfacial charge recombination between the conduction band electrons and triiodide ions in the electrolyte. On the other hand, different ratios caused different shift directions of the TiO2 conduction band, which was confirmed by charge transport resistance obtained also from EIS analysis. To be specific, when the ratio of N719-to-DPPA was 2:1 and 1:1, the conduction band of TiO2 film was positively shifted, while it was negatively shifted when the ratio was 4:1. (C) 2010 Elsevier Ltd. All rights reserved,