Molecular design towards suppressing electron recombination and enhancing the light-absorbing ability of dyes for use in sensitized solar cells: a theoretical investigation

Abstract

The recombination rates of two typical D–π–A dyes have been evaluated qualitatively by means of quantum chemical calculations. By dissecting the geometrical and electronic structures of the dyes, the function of the inserted phenyl ring in inhibiting recombination is recognized as the blocking of back electron transfer and decreasing the HOMO distribution on the anchoring group, but with the distorted structure caused by the inserted benzene ring also decreasing the light harvesting ability. Molecular designs for the screening of potential dyes are carried out with a comprehensive consideration of both suppressing recombination and enhancing light absorption. Tightening the adjacent rings in the donor and π-spacer is verified to be a feasible route for extending the π-conjugation, thus leading to red-shifted and broad absorption spectra. The calculated results show that the dyes possessing both a small distribution of the HOMO on the anchoring group and a relatively strong light harvesting ability are the most promising candidates for use in dye-sensitized solar cells. Moreover, this work provides a deep understanding of the relationship between the electron recombination rate and electronic structure of dyes, and provides theoretical guidelines for the design of high performance sensitizer materials.