Theoretical Studies On The Performance Of Rhenium Complexes As Dye Sensitizer

With the excessive demand and consumption of energy,development and utilization of renewable energy sources andcorresponding materials become a very active topic in the world.Among them, solar energy is the first option that the mankind usesto deal with the energy crisis. Recently, dye sensitizer solar cell(DSSC) is attracting great interest from scientists for its charactersof low cost in an environmentally friendly way. But so farsolar-to-electricity conversion effciency of DSSC is still low. Thekey of the research work is how to improve the conversioneffciency. Because the dye-sensitizer plays a key role in thesolar-to-electricity conversion and electronic transportmechanisms, development and synthesis of new high efficiency dyesensitizer is expected to increase the efficiency of DSSC.Ru (II) complexes have been extensively investigated as dyesensitizers in DSSC, meanwhile, Re (I) complexes also have widelyattracted owing to their long-term stability of chemistry andphotochemistry properties, relatively long-lived excited states,higher oxidation-reduction potentials and strong absorption in thevisible range. These investigations of rhenium complexes will bebeneficial to the development of novel and high performance of dyesensitizer. Rapid development of computer technology makes theoretical calculation more accurate and reliable. The theoreticalcalculation not only provides theoretical complement forexperiment, but also provides the feasible theoretical guidance forthe experimental workers. So the experimental cost is reduced andthe work efficiency is also improved.In the work, the main research focus on the variation of ligand todesign and develop new and high efficiency Re (I) complexes as dyesensitizers. The method of quantum chemistry calculation is mainlyused by the investigation starting from the electronic structure ofmolecules and considering the solvent effects. The ground-andexcited-state structures and spectroscopic properties of designeddye-sensitizers are deeply analyzed. And the influences of dyesensitizer on the related parameters about efficiency of DSSC arealso discussed in detail. Moreover, the relationship betweengeometrical structure and photoelectric properties is essentiallyexplained. And the performance of the designed dye sensitizer isalso predicted. We hope that this work can provide theoreticalguidance and new ideas for designing, synthesis and application ofnew materials with better performance. The main contents are asfollows:1. The effect of the different number and positions of carboxylgroup on phenanthroline ligand on electronic structures,spectroscopic properties of rhenium (I) tricarbonyl complexesRe(CO)3Cl(HnL) have been investigated theoretically by DFT andTDDFT. The related parameters were calculated to assess thepotential applications of dye sensitizer in DSSC. The results showthat the different number and positions of carboxyl group can change the nature of the frontier molecular orbital, particularly,LUMO. And it can change the light-absorbing and electronictransport ability of dye sensitizer and efficiency of DSSC. The newdesigned a2and b9may have better performance as the dyesensitizer than other designed dyes.2. The introducing different electron-withdrawing andelectron-donating groups on Phen ligand effect on electronicstructures, spectroscopic properties of rhenium (I) tricarbonylcomplexes as dyes in DSSC have been investigated theoretically.The results show that the increasing of electron-withdrawing abilityobviously decreases the energy of LUMO and the energy gapbetween HOMO and LUMO. With the increasing ofelectron-withdrawing properties of functional groups, theabsorption spectra have obvious red-shift. The order is D2<D3<D4<D1<D4<D6<D7, which is consistent with the increasing ofelectron-withdrawing ability. In addition, comparing with thecalculated related parameters, the new designed D5may havebetter performance as the dye sensitizer than other designed dyes.