Theoretical study on novel double donor-based dyes used in high efficient dye-sensitized solar cells: The application of TDDFT study to the electron injection process

The geometries and electronic structures of organic dye sensitizers, CCT1A, CCT2A, CCT3A, CCT1PA, and CCT2PA comprising double-donor groups, π-spacer, and acceptor group forming D–D–π–A system, were studied using DFT and TDDFT. The calculated results have shown that TDDFT calculation using a newly-designed functional which takes into long-range interaction, CAM-B3LYP, was reasonably capable of predicting the excitation energies and the absorption spectra of the molecules. The adsorption of these dyes on the TiO2 anatase (1 0 1) surface and the electron injection mechanism were also investigated using a dye-(TiO2)38 cluster model, employing PBE and TD-CAM-B3LYP calculations, respectively. The adsorption energy (Eads) of CCTnA (n = 1–3) was calculated to be −15.26, −18.93, and −20.12 kcal/mol respectively, indicating strong adsorption of dye to a TiO2 surface by carboxylate groups. These calculated results suggested that the CCT3A is a promising candidate for highly efficient DSSCs. It was shown that the electron injection mechanism occurs by direct charge-transfer transition in a dye-TiO2 interacting system, resulted in the stronger electronic coupling strengths of the anchoring group of the dyes and the TiO2 surface which corresponded to higher observed Jsc as expected in CCT3A dye. Through a combined theoretical and experimental investigation we have shown that the trend of charge-injection efficiency in dye-sensitized solar cells constituted from dyes is determined by the adsorption energy of dye-(TiO2)38 complexes.

The CCT3A is a promising candidate for highly efficient DSSCs which can efficiently inject electron from LUMO orbital of dye to CB of TiO2 and also cover absorb the UV/Vis and near IR range. Our theoretical models are proper to be guidelines for selecting the suitable π-spacer and anchor moiety to be used for further improved sensitizers in DSSC applications.Figure optionsDownload as PowerPoint slideHighlights
► The predicted coupling strengths of dye-TiO2 can be related to experimental Jsc.
► The electron injection mechanism can be performed by TDDFT using CAM-B3LYP.
► Our model can be guidelines for improving sensitizers in DSSC applications.
► We performed the newly designed dye with conversion efficiency up to 98.3% of N3.