Sensitization Mechanism Of Tris (8-hydroxyquinoline) Iron (Ⅲ) On TiO₂ Anatase (101) Surface

Abstract: Recently, academic and commercial interests have been paid on dye-sensitized solar cells (DSSCs), DSSCs has become a strong competitor for the new energy field. Compared with other commercial silicon solar cells, DSSCs possesses many advantages such as high photoelectric conversion efficiency, simple assemble technology, excellent electrochemical stability, abundant raw materials, low cost and environmental friendliness. In this paper, the DSSCs development and common sensitizers were reviewed firstly, then we adopt the tris (8-hydroxyquinoline) iron(â…¢) complexes series as sensitizers in dye-sensitized solar cells to investigate the sensitized mechanism, the structure and electrochemical performance of tris (8- hydroxyquinoline) iron(â…¢) complexes series were discussed detaildely. We studied the tris (8- hydroxyquinoline) iron(â…¢) complexes series in theory according to the research focus and its defects as sensitizers of DSSCs.Density functional theory (DFT) in periodic DMol³ program was employed to investigate the sensitization mechanism and electronic structural of tris ( 8- hydroxyquinoline -5- carboxylic acid) iron (â…¢), tris (8- hydroxyquinoline -7- carboxylic acid) iron(â…¢) and tris ( 8- hydroxyquinoline -5- sulfonic acid) iron(â…¢) on TiO₂ anatase (101) surface. These sensitizers possesses a very small HOMO (the highest occupied molecular orbital)- LUMO(the lowest unoccupied molecular orbital) energy gap, and this allows for easy electron excitation from HOMO to the LUMO. As the nanocrystalline TiO₂ adsorbs the sensitizer, the energy of the HOMO level, the LUMO and Fermi level increase, These changes lead to an enhancement of the open-circuit photovoltage (VOC) in dye-sensitized TiO₂ solar cells.In addition, we theoretically determined the sensitization mechanis+m of tris (8- hydroxyquinoline -5- carboxylic acid) iron (â…¢) and tris (8- hydroxyquinoline -7- carboxylic acid) iron(â…¢) dyes that are attached by carboxylic acid anchor groups to TiO₂ anatase (101) surface; But tris ( 8- hydroxyquinoline -5- sulfonic acid) iron(â…¢) dyes are attached by sulfonic acid anchor groups to TiO₂ anatase (101) surface. The Energy gap of tris (8- hydroxyquinoline -7- carboxylic acid) iron(â…¢) dyes is larger than the other two sensitizers, and can match the ELUMO level of TiO₂ very well. tris (8- hydroxyquinoline -7- carboxylic acid) iron(â…¢) adsorption more negatively shifted the Fermi level than the other sensitizers adsorption, which corresponded to the enhancement of the Voc values. Consequently, the molecular adsorption of tris (8- hydroxyquinoline -7- carboxylic acid) iron(â…¢) is energetically more favoured than those of the other adsorbed molecules.