A Combined Experimental and Computational Investigation of Anthracene Based Sensitizers for DSSC: Comparison of Cyanoacrylic and Malonic Acid Electron Withdrawing Groups Binding onto the TiO2 Anatase (101) Surface

Four anthracene based sensitizers, 3-(anthracene-9-yl)-2-cyanoacrylic acid ( M1 ), 2-cyano-3-(10-methoxyanthracene-9-yl)acrylic acid ( M2 ), 2-(anthracene-9-ylmethylene) malonic acid ( M3 ), and 2-((10-methoxyanthracene-9-yl)methylene)malonic acid ( M4 ) were designed and synthesized to understand the binding modes of anchoring groups ( and ) on the nanocrystalline TiO 2 (101) surface and on the efficiency of dye-sensitized solar cells (DSSCs). All four sensitizers have been fully characterized using ATR-FTIR, UV−vis, and CV. These sensitizers were tested in DSSCs using 0.05 M I 2, 0.5 M 1,2-dimethyl-3- n -propylimidazolium iodide (DMPI), and 0.5 M lithium iodide (LiI) in methoxypropionitrile (MPN) redox electrolyte. The sensitizers having a monocarboxylic acid group, i.e., M1 and M2, have shown marginally higher IPCE and efficiency than M3 and M4 having dicarboxylic acid groups. To have a detailed understanding of this behavior, the adsorption and binding energies to the TiO 2 surface of these dyes have been investigated using computational techniques (periodic DFT). The studies show that the cyanoacrylic acid anchoring group has a stronger binding to the TiO 2 surface compared to the malonic acid anchoring group.