| Property | Description |
| Property #1 | The dye has to be luminescent. |
| Property #2 | The absorption spectra of the dye has to include ultraviolet-visible (UV-vis) and near-infrared region (NIR) regions. |
| Property #3 | The highest occupied molecular orbital (HOMO) has to be found far from the surface of the conduction band of TiO2 and the lowest unoccupied molecular orbital (LUMO) has to be located as near to the surface of the TiO2, and then has to be higher with respect to the TiO2 conduction band potential. |
| Property #4 | HOMO should lie lower than that of redox electrolytes. |
| Property #5 | The periphery of the dye has to be hydrophobic to improve the long-term stability of cells, since it conducts to reduced direct contact among electrolyte and anode; if not, water-induced distortion of the dye from the TiO2 surface may take place, which may diminish the stability of cells. |
| Property #6 | To avert the accumulation of the dye over the TiO2 surface, co-absorbents such as chenodeoxycholic acid (CDCA) and anchoring groups like alkoxy-silyl [24] , phosphoric acid [25] , and carboxylic acid group [26] [27] were integrated among the dye and TiO2. This leads to the prohibition of dye gathering and therefore restricts the recombination reaction [28] among redox electrolyte and electrons in the TiO2 nanolayer as well as conducts to the generation of stable linkage. |