Effects of carboxylic acid and phosphonic acid anchoring groups on the efficiency of dye sensitized solar cells: A computational study

• Adsorption of different carboxylic acid linkers and different phosphonic acid linkers on anatase TiO2 surface.
• Electronic structure of the surface and changes in the HOMO and LUMO of the linkers on the TiO2surface are investigated.
• Use of carboxylic acid and phosphonic acid linkers for the application in DSSCs are compared.
• Possible reasons for low performance of Phosphonic acid linkers are suggested.

In axially coordinated DSSCs the dye is attached to the surface via linker and the linker play a role of a conductor of electron and a bridge to the surface which has a very important effect on the efficiency of the cell. It has been shown that using one particular dye with different linkers could result in different efficiencies. In this paper, using density functional theory, different carboxylic acid (CA) linkers, and different phosphonic acid (PA) linkers are studied and their effects on the electronic structure of the surface and changes in the HOMO and LUMO of the linkers due to adsorption on the surface are investigated. For each family of linkers, based on calculations, the best one to be used in axially coordinated DSSCs is suggested. Comparing these two families, carboxylic acid linkers show superior properties in terms of cell efficiencies. phosphonic acid linkers, however, are shown to strongly bond to surface while resulting in lower conversion efficiencies compared to the carboxylic acid linkers the reason of which is still a question. Based on calculation of the changes in properties of the surface and properties of phosphonic acid linkers some reasons behind their low performances are suggested.

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