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We have previously reported the efficiency enhancement of gel electrolyte-based SnO 2 Dye-sensitized Solar Cells (DSCs) through the use of an ultra-thin (∼5 nm) coverage of the SnO 2 nanopaticles with CaCO 3 in order to reduce the surface recombination. Also, we have reported the effect of the salt used in the gel electrolyte on the efficiency of these devices. Another vital component of the DSCs is the dye used for light absorption. In our previous studies, the indoline dye D358 was primarily used because of its relatively strong anchorage on to the nanoparticles. However, the absorption spectra of the other dyes in the indoline dye family such as D149 and D131 indicate that they have complementary absorption in the visible region suggesting that, a mixture of these dyes could produce better efficiencies. We have observed a significant improvement in efficiency of these devices when a double-dye sensitization is employed. We have attempted to interpret the observed results using the molecular geometry and other properties of the dyes. We used a 1:1 double-dye mixture having combinations of D358, D149 and D131 in DSC devices based on CaCO 3 coated SnO 2 . Among the different combinations, D149/D131 mixture gave the best efficiencies. This device produced efficiencies of 5.10% and 4.80% for a liquid and a gel electrolyte respectively under 1.5 AM (100 mW cm −2 ) simulated sunlight. The general trend of the observed results indicates that there is an efficiency enhancement of about 30% for the D149/D131 mixture compared to their respective individual performances. [ABSTRACT FROM AUTHOR]