The influence of a dye–TiO2 interface on DSSC performance: a theoretical exploration with a ruthenium dye

Abstract

Density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches were applied to explore the influence of a dye–TiO₂ interface on DSSC performance by taking a heteroleptic Ru(II) dye as an example. Our analysis was based on the interpretation of the dye–TiO₂ geometry, electronic structure, and light harvesting and utilization. The results indicate that an alkaline electrolyte is necessary if the solar cell was fabricated with an Ru dye coordinated to 2,5-bis(N-pyrazolyl)pyridine and bipyridine ligands. The higher average thermodynamic driving force of the a@(TiO₂)₅(OH) structure ensures a better electron injection ability. Proper modification of the acceptor ligand (4-carboxyl-pyridine fragment) not only expands the absorption coverage, but also improves the ability to capture more photons within effective absorption bands. Despite the absorption coverage being further expanded within the c@(TiO₂)₅(OH) geometry, the relatively weaker molar absorption coefficient reduces the light harvesting capability. The extra absorption bands in the lower energy region indicate more photons will be captured in the b@(TiO₂)₅(OH) structure, therefore leading to a higher short-circuit current density. Our results elucidate the effect of the dye–TiO₂ interface on DSSC performance and supply a promising way to estimate and screen possible candidates for DSSC application.