Substituent effects on the croconate dyes in dye sensitized solar cell applications: a density functional theory study.

Using the density functional theory (DFT), we studied two model croconate dyes, one with an electron-donating substituent (CR1) and the other with an electron-withdrawing group (CR2). The geometric, electronic, and optical properties of these dyes were compared. Upon switching from CR1 to CR2, a considerable bathochromic shift was observed in the electronic absorption spectrum. We also investigated the adsorption behavior of the two dyes on a TiO2 (101) anatase surface by employing periodic DFT simulations. The periodic electronic-structure calculations revealed that the diketo group of CR1 bound more strongly to the TiO2 surface than that of CR2, with a binding strength comparable to that of a typical organic D-π-A dye. In this work we evaluate in particular the effect of the electron withdrawing/donating nature of the substituent on the electronic, optical, and adsorption properties of the croconate dyes. Finally, we hope that the present study will help in the design of highly efficient dyes for dye sensitized solar cells by considering substituent effects. Graphical abstract Effect of substituent on binding energy and charge transfer.