Dye sensitized solar cells : dyes and anchoring groups -

Abstract

Dye-sensitized solar cells (DSSCs) have attracted much attention due to their relatively low cost, acceptable conversion efficiency and ease of fabrication. Several attempts were made in order to increase the light-harvesting efficiency of solar cells mainly the engineering of panchromatic dyes (sensitizers). One of the main functional moieties in a sensitizer is the anchoring group; the group that functions as the adsorption site of the dye to the semi-conductor. In the chemical literature many examples of anchoring groups have been proposed, ranging from carboxylic and phosphonic acids to pyridyl N-oxide, pyridine, and azoles. In an attempt to investigate the effect of different anchoring groups on the performance of DSSCs, we present the synthesis of two different dyes T181 and T182 with pyridine and pyridine oxide anchoring groups, respectively. Moreover, the pyridine-based dye T181, which binds to the Lewis-acid sites of TiO2 was co-sensitized with commercial dyes YD2 and DB having carboxylic acid anchoring groups, which bind to the Brønsted-acid sites of TiO2 in order to increase the efficiencies of DSSCs by enhancing the light harvesting efficiency and reducing unwanted recombination reactions. An increase in the total cell efficiency was seen for the T181-DB and T181-YD2 co-sensitized cells in two different iodine-based and cobalt-based electrolytes. The difference in enhancement between the T181-DB and T181-YD2 DSSCs was due to different total dye loading in the co-sensitized films. In the T181-DB cell the amount of adsorbed T181 and DB was equal to the sum of the dyes’ loadings found in the non-co-sensitized films, unlike the T181-YD2 one where less of T181 was adsorbed due to non-complementary sizes of the two dyes. In the cobalt-based electrolyte system, more enhanced photocurrent and photovoltage of the two co-sensitized cells were seen compared to the iodine-based electrolyte system because of the effect of the extended linker fragment in T181, which is more effective with the cobalt el