Density functional theory as a guide for the design of pyran dyes for dye-sensitized solar cells

Using density functional theory and hybrids, we examined several derivatives of the dye 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)- 4H-pyran, with the objective of identifying modifications which would improve the properties of dyes for dye-sensitized solar cells. We calculated the electronic structure of numerous derivatives at the HOMO and LUMO energy levels, with the hypothesis that directing the flow of excited electrons to the point of the dye at which the molecule attaches to TiO₂ would increase the energy conversion efficiency of the cell. We also examined the UV-visible absorption spectra of the dyes, with the objective of capturing the maximum amount of solar light. By use of the derivatives we compared the use of two electron-donating groups instead of one, extension of the conjugated chain leading to the attachment point of the dye, use of oxygen versus sulfur or selenium in the dye, and the use of different electron-donating groups. We identified several promising donating groups and determined that the other modifications to the dye are likely to increase solar cell efficiency. Graphical Abstract: [Figure not available: see fulltext.]